No CrossRef data available.
Published online by Cambridge University Press: 08 January 2003
In Pötscher (1991, Econometric Theory 7, 163–185) the asymptotic distribution of a post-model-selection estimator, both unconditional and conditional on selecting a correct model (minimal or not), has been derived. Limitations of these results are (i) that they do not provide information on the distribution of the post-model-selection estimator conditional on selecting an incorrect model and (ii) that the quality of this asymptotic approximation to the finite-sample distribution is not uniform with respect to the underlying parameters. In the present paper we first obtain the unconditional and also the conditional finite-sample distribution of the post-model-selection estimator, which turn out to be complicated and difficult to interpret. Second, we obtain approximations to the finite-sample distributions that are as simple and easy to interpret as the asymptotic distributions obtained in Pötscher (1991) but at the same time are close to the finite-sample distributions uniformly with respect to the underlying parameters. As a by-product, we also obtain the asymptotic distribution conditional on selecting an incorrect model.We thank the co-editor Richard Smith and the two referees for helpful comments on a previous version of this paper. Hannes Leeb's research was supported by the Austrian Science Foundation (FWF), project P13868-MAT.
The traditional theory of parametric statistical inference is primarily concerned with statistical properties of estimators and inference procedures, such as tests or confidence sets, under the central assumption of an a priori given model. That is, it is assumed that the model is known to the researcher prior to the statistical analysis, except for the value of the true parameter vector. In practice, however, the specification of the model (choice of functional form, choice of regressors, number of lags, etc.) is often also determined only after the data have been observed, violating the central assumption of an a priori given parametric model. As a consequence, the actual statistical properties of estimators or inference procedures following such a data-driven model selection step are not described by the traditional theory assuming an a priori given model; in fact, they may differ substantially from the properties predicted by the traditional theory (cf. Pötscher, 1991, Sect. 3.3). Ignoring the additional uncertainty originating from the data-based model selection step and (inappropriately) applying traditional theory can hence result in very misleading conclusions.
Sen (1979) obtains the unconditional asymptotic distribution of a post-model-selection estimator in an independent and identically distributed (i.i.d.) maximum likelihood framework when there are two competing models. In Pötscher (1991) the asymptotic properties of a class of post-model-selection estimators (based on a sequence of tests) are studied in a rather general setting covering nonlinear models, dependent processes, and more than two competing models.1
For further results in this direction see Kabaila (1995), Pötscher (1995), and Pötscher and Novak (1998).
They do not provide information on the distribution of the post-model-selection estimator conditional on selecting an incorrect model. Although asymptotically such models are never selected by any reasonable model selection procedure, including the one considered in Pötscher (1991), the finite-sample probability of selecting an incorrect model can be substantial (see, e.g., Pötscher and Novak, 1998, Table II).
The approximation to the finite-sample distribution provided by the asymptotic distribution obtained in Pötscher (1991), although of reasonably good quality in many cases, can be very poor in others (cf. the Monte Carlo results in Pötscher and Novak, 1998). As argued in Pötscher (1991) and Pötscher and Novak (1998), this is related to certain aspects of nonuniformity in the convergence of the finite-sample distributions.
In the present paper we take a closer look at the distribution of post-model-selection estimators within the more restricted framework of a linear regression model Y = Xθ + ε. As in the aforementioned papers, the model selection procedure considered here is a “general-to-specific” testing procedure, and the competing models are assumed to form a nested sequence. This framework is general enough to cover some practically relevant cases such as, e.g., model selection in distributed lag models or polynomial regression. At the same time it is simple enough to be amenable to mathematical analysis, allowing one to gain theoretical insight into the intricate properties of post-model-selection estimators. We first obtain the conditional and the unconditional finite-sample distributions and densities of the post-model-selection estimator

. This represents a major step forward in the pretesting literature.
2There is a substantial body of literature on pretest estimators as summarized in Judge and Bock (1978), Judge and Yancey (1986), Giles and Giles (1993), and Magnus (1999). This literature mainly concentrates on risk properties of pretest estimators but does not provide results on finite-sample distributions. The only exceptions we are aware of are Giles and Srivastava (1993), who consider a very limited special case, and Elsinger (1994) (cf. Remark 6.3(ii)).

conditional on selecting the first p regressors is quite complicated and hence difficult to interpret (cf. expressions (23) and (24) in Section 3). The density of the corresponding asymptotic conditional distribution can be obtained from Pötscher (1991) in case the selected model is correct (i.e., all relevant regressors have been selected for inclusion [cf. (28) and (29) in Section 4]). It is much simpler than the finite-sample density but at the expense of not providing an approximation that is uniformly close to the finite-sample density when the regression parameter varies. In particular, it sometimes misses essential features of the finite-sample density. It turns out, however, that a quite simple and easy to interpret uniform approximation capturing all the essential features of the conditional finite-sample distribution can be found. We start from the observation that the (conditional) finite-sample density fn,θ,σ*(·|p) of the idealized post-model-selection estimator

, which uses knowledge of the error variance σ2, is of a quite simple form. We then show in Theorem 4.2 in Section 4 that fn,θ,σ*(·|p) provides a uniform approximation to the (conditional) finite-sample density fn,θ,σ(·|p) of the post-model-selection estimator

. Because of its simplicity and the uniformity, this approximation then allows one easily to get insight into the behavior of the much more complicated finite-sample distribution of the post-model-selection estimator

.
Whereas the asymptotic distribution of the post-model-selection estimator conditional on selecting a correct model is relatively easy to obtain (even in more general frameworks [cf. Sen, 1979; Pötscher, 1991]), the asymptotic distribution conditional on selecting an incorrect model (i.e., conditional on not selecting all relevant regressors for inclusion) is much harder to derive, as a result of the fact that the conditioning event has limiting probability zero.3
Sen (1979) studies the unconditional asymptotic distribution also when the true parameter is local to the smaller of the two competing models. From his derivation the asymptotic distribution conditional on selecting the smaller model could be easily obtained. However, in this local alternatives framework the limiting probabilities of selecting either one of the two competing models are positive.
Apart from being of interest in their own right, the results obtained in the present paper have a number of important applications and ramifications.
Pötscher (1991) finds considerable discrepancy between the asymptotic distribution of the post-model-selection estimator and the normal approximation provided by the classical asymptotic theory based on the premise of an a priori given model. The present paper confirms this finding for the finite-sample distributions (cf. also the discussion surrounding (13), (23), and (24)).
In practice often the standard confidence intervals based on classical least-squares theory are reported even in cases where pretests have been conducted. The finite-sample distributional results obtained in the present paper (cf. (12), (17), (23), and (27)) can be used to calculate the actual coverage probability of these confidence intervals and thus allow one to assess the impact of model selection on standard inference procedures. Cf. Pötscher (1991), Section 3.3, for some related numerical results based on the (conditional) asymptotic distribution.
The finite-sample distributions obtained in the present paper can be used quite easily to calculate (conditional and unconditional) moments of the post-model-selection estimator. This will be discussed in detail elsewhere.
The uniform approximation results that appear later in this paper (e.g., Theorems 4.2 and 5.2) and the limiting results under local alternatives (Corollaries 4.5 and 5.4) provide stepping-stones for the results in Leeb and Pötscher (2001), which concern properties of estimators for the finite-sample distribution of post-model-selection estimators. Whereas it is easy to obtain consistent estimators in a number of ways, a remarkable result from Leeb and Pötscher (2001) shows that (locally) uniformly consistent estimation is impossible.
The plan of the paper is as follows. After introducing the model and the post-model-selection estimator in Section 2, we obtain the conditional and the unconditional finite-sample distribution of the post-model-selection estimator (and of its idealized version) in Section 3. The results in this section provide, in particular, a substantial extension of the results in Giles and Srivastava (1993), where a model with a constant and only one regressor is considered (cf. Remark 6.3(ii)). Section 4 studies the uniform approximation to the conditional finite-sample distribution of the post-model-selection estimator

mentioned previously (Theorem 4.2). In Corollary 4.5 the asymptotic conditional distribution is obtained, including the case where one conditions on selecting an incorrect model. Furthermore, regions over which convergence to the asymptotic distribution is uniform/nonuniform are also identified (Corollary 4.6 and its discussion). Analogous results for the unconditional distribution and the selection probabilities are given in Section 5. Section 6 contains some remarks and extensions. Conclusions are drawn in Section 7. Proofs are relegated to the Appendixes.
Consider the linear regression model

where X is a nonstochastic n × P matrix with rank(X) = P and ε ∼ N(0,σ2In), σ2 > 0. Here n denotes the sample size and we assume n > P ≥ 1. For the asymptotic results in Sections 4 and 5 we shall in addition assume that Q = limn→∞ X′X/n exists and is nonsingular for simplicity, although this assumption is not needed in its full strength for all of the asymptotic results (cf. Remark 6.2(ii)). Similarly to the procedure in Pötscher (1991), we consider model selection from a collection of nested models M0 ⊆ M1 ⊆ ··· ⊆ MP that are given by

Hence, model Mp corresponds to the situation where only the first p regressors in (1) are included. Note that M0 = {0} and MP = RP. We call Mp the regression model of order p.
The following notation will prove useful. For matrices A and B of the same row-dimension, the column-wise concatenation is denoted by (A : B). If C is an n × P matrix, let C[p] denote the n × p matrix consisting of the first p columns of C. Similarly, let C[¬p] denote the n × (P − p) matrix consisting of the last P − p columns of C. If x is a P × 1 vector, we write in abuse of notation x[p] and x[¬p] for (x′[p])′ and (x′[¬p])′, respectively. (We shall use these definitions also in the “boundary” cases p = 0 and p = P. It will always be clear from the context how expressions containing the symbols C[0] , C[¬P] , x[0] , and x[¬P] are to be interpreted.) As usual, if x is a vector, the jth component of x will be denoted by xj. Using the preceding notation, the restricted least-squares estimator using only the first p regressors is given by

for p ≥ 1 and by

for p = 0.
Given a parameter value θ, its order is defined as

Hence, if θ is the true parameter value, only models Mp with p ≥ p0(θ) are correct models. We stress that p0(θ) is a property of a single parameter value and hence needs to be distinguished from the notion of the order of the model Mp introduced earlier, which is a property of the set Mp.
A model selection procedure in general is now nothing else than a data-driven (measurable) rule

that selects a value from {0,…,P} and thus selects a model from the list of candidate models M0,…,MP. In this paper, we shall consider a model selection procedure based on a sequence of hypothesis tests, which is given as follows. The sequence of hypotheses H0p : θ ∈ Mp−1 is tested against the alternative H1p : θ ∈ Mp[setmn ]Mp−1 in decreasing order starting at p = P until the first rejection occurs. If H0p is the first hypothesis in this process that is rejected, we set

. If no hypothesis is rejected we set

. (The case where a subvector of θ is assumed to be common to any submodel and hence is not subject to test is discussed in Remark 6.3(i).) Each hypothesis in this sequence is tested by a kind of t-test where the error variance estimator is always taken from the overall model. More formally, we have

where the test statistics are given by

with

being the square root of the pth diagonal element of the matrix indicated and with

The critical values cp are independent of sample size n (cf., however, Remark 6.2(i)) and satisfy 0 < cp < ∞ for 1 ≤ p ≤ P. We also set T0 = c0 = 0 to ensure a well-defined

. Note that under the hypothesis H0p the statistic Tp is t-distributed with n − P degrees of freedom for 1 ≤ p ≤ P.
The post-model-selection estimator

is now defined as follows. The first

coordinates of

are given by the restricted least-squares formula based on the first

regressors, and the remaining

coordinates are set equal to zero. That is,

is the P × 1 vector given by

For theoretical reasons we shall also be interested in the idealized model selection procedure that assumes knowledge of σ2 and hence uses Tp* instead of Tp, where

and T0* = 0. The corresponding model selector is denoted by

and the resulting idealized post-model-selection estimator by

. Note that under the hypothesis H0p the variable Tp* is standard normally distributed for 1 ≤ p ≤ P.
We conclude this section by introducing some further notation. For p ≥ 1, the expected value of the restricted least-squares estimator

given by (2) will be denoted by μn(p) and is given by

In case p = P, the second term on the right-hand side (r.h.s.) of (6) and similar expressions are to be interpreted as zero; i.e., μn(P) = θ[P] = θ. As usual, the jth component of μn(p) will be denoted by μn,j(p). We note that μn(p) depends on θ, although this dependence is not shown explicitly in the notation. The distribution of

is normal with mean zero and variance-covariance matrix σ2(X [p]′X [p]/n)−1. The cumulative distribution function (c.d.f.) and probability density function (p.d.f.) of this distribution, respectively, will be denoted by Φn,p and φn,p. Their corresponding large-sample limits, i.e., the c.d.f. and p.d.f. of a normal distribution with mean zero and variance-covariance matrix σ2limn→∞(X [p]′X [p]/n)−1, will be denoted by Φ∞,p and φ∞,p, respectively. As usual, the c.d.f. and p.d.f. of the standard normal distribution on the real line will be denoted by Φ and φ, respectively. We shall also use Δ(a,b) with a ∈ R ∪ {−∞,∞} and b ∈ R as shorthand notation for Φ(a + b) − Φ(a − b) with the usual convention that Φ(∞) = 1 and Φ(−∞) = 0.
In a more general framework, allowing for nonlinear models and also for dependent data, Pötscher (1991) obtains the asymptotic distribution of the post-model-selection estimator conditional on the event of choosing a correct model Mp (i.e., p ≥ p0(θ)) and also the unconditional asymptotic distribution.4
See also Appendix A of Pötscher and Novak (1998) for a relaxation of an unnecessarily restrictive assumption in Pötscher (1991).
PROPOSITION 3.1. For every p, 0 ≤ p ≤ P, the random quantities

, and

are mutually independent. In particular,

is independent of {Tp+1,…,TP} and also of {Tp+1*,…,TP*}. Furthermore, T1*,T2*,…,TP* are mutually independent.
Inspection of the proof in Appendix A shows that in fact for every p, 0 ≤ p ≤ P, the collection

is independent of

and that the collection

is independent of

.
In this section we assume that σ2 is known and we obtain the finite-sample distribution of

, the idealized version of the post-model-selection estimator. The distribution function of

conditional on selecting model order p, i.e., conditional on

, is considered first and satisfies

for 1 ≤ p ≤ P and is equal to point mass at zero if p = 0. Here Pn,θ,σ denotes the probability measure under the true parameters θ and σ. Furthermore, R+ is the set of nonnegative real numbers, and we use the convention that the indicator function 1R+P−p(·) is identically equal to one if p = P. It suffices now toconcentrate only on the case p ≥ 1, and in this case we will consider a centered and scaled version of (7), namely,

where μn(p) is given by (6). We recall that μn(p) is the unconditional mean of the restricted least-squares estimator

and satisfies μn(p) = θ[p] whenever p ≥ p0(θ). The centering and scaling applied in (8) are of course only of trivial consequence for the finite-sample results but will prove useful for the asymptotic analysis (cf. also Remark 6.1 on centering constants). We hence only need to evaluate

with t ∈ Rp. For convenience we shall also refer to (9) as the conditional distribution of the idealized post-model-selection estimator

. Now, in light of Proposition 3.1,
As a point of interest we note that (10), and hence (12), as follows, are not affected by the tests based on Tp+1,…,TP at all. Recalling that Φ denotes the c.d.f. of a standard normal random variable and that Δ(a,b) = Φ(a + b) − Φ(a − b), the denominator on the far r.h.s. of (10) is easily seen to be equal to 1 − Δ(−n1/2μn,p(p)σ−1ξn,p−1,cp), because Tp* is normally distributed with mean n1/2μn,p(p)σ−1ξn,p−1 and variance 1. The numerator can be written as

and where φn,p is the p.d.f. of

(cf. Section 2). From (10) and (11) the density fn,θ,σ*(t|p) of Fn,θ,σ*(t|p) is now easily obtained as

The conditional density of

is thus seen to be an excised normal density, the denominator in (12) being just a normalizing constant. The excision interval is centered at −n1/2μn,p(p). In case μn,p(p) = 0, which is in particular the case if p > p0(θ), the conditional density in (12) simplifies to

which is symmetric about t = 0. It should also be noted that (13) depends on sample size only through the matrix (X [p]′X [p]/n)−1 and through the square root of its last diagonal element ξn,p, both of which stabilize at their limits as the sample size increases (given X′X/n → Q). However, in case μn,p(p) does not vanish, which is typical for the case p ≤ p0(θ), (12) shows a further and more important sample-size dependence of fn,θ,σ*(·|p) in that the center of the excision interval, i.e., −n1/2μn,p(p), will typically diverge to ±∞. Furthermore, note that (13) is independent of θ, whereas in general (12) depends on θ through μn,p(p). See Section 4 for more discussion.
Not too surprisingly, (13) coincides with the asymptotic distribution of the post-model-selection estimator obtained in Pötscher (1991, equation (2)) in case p > p0(θ), except that the matrix σ2(X [p]′X [p]/n)−1 replaces the asymptotic variance-covariance matrix of the restricted estimator in the latter reference. As a consequence, all further derivations in Pötscher (1991) based only on this distribution apply also to the conditional finite-sample distribution of the post-model-selection estimator

if p > p0(θ). In particular, the numerical results in Section 3.3 of Pötscher (1991) demonstrating the considerable discrepancy between the asymptotic distribution of the post-model-selection estimator conditional on

and the distribution of the restricted estimator treating p as given directly apply here to the comparison of the conditional finite-sample distribution of

with the finite-sample distribution of the restricted least-squares estimator

.
The unconditional finite-sample distribution of

can now easily be expressed in terms of the conditional distributions Fn,θ,σ*(·|p) and the selection probabilities

. Let

with u ∈ RP denote the unconditional c.d.f.. (Again, centering and scaling are of no consequence for the finite-sample results but will prove useful in later sections [cf. also Remark 6.1].) Using (7) and (9) we obtain

where we use the convention that Fn,θ,σ*(·|0) ≡ 1. Observe that the expressions θ[p] − μn(p) and θ[¬p] in (14) vanish for p ≥ p0(θ). In view of Proposition 3.1, the selection probabilities πn,θ,σ*(p) can be expressed as

with

and Pn,θ,σ(|T0*| ≥ c0) = 1. (Here and in the sequel we use the convention that products such as the one on the r.h.s. of (15) are set equal to 1 in case p = P.) Note that the selection probabilities are all positive for each n and that for j > p0(θ) the probability in (16) simplifies to Δ(0,cj), which is nothing else than 1 minus the significance level of the test based on Tj*. Plugging (10), (15), and (16) into (14) gives the alternative expression
with the convention that the integral in (17) is to be interpreted as 1 when p = 0. As noted in the introduction, the finite-sample c.d.f. (17) can, e.g., be used to assess the actual coverage probabilities of the standard confidence intervals that do not account for model selection. Furthermore, (17) enables the computation of moments (e.g., bias, variance) of the post-model-selection estimator. This will be discussed in detail elsewhere.
In this section we consider the finite-sample distribution of the post-model-selection estimator

. Again

for 1 ≤ p ≤ P holds, and the distribution of

conditional on

is point mass at zero. Proceeding similarly as before, in case p ≥ 1 we may instead consider

It hence remains to evaluate

where t ∈ Rp. For convenience we shall again also refer to (20) as the conditional distribution of

. Now
where A is shorthand for the event {|Tp| ≥ cp,|Tp+1| < cp+1,…,|TP| < cP} and h denotes the density of

, i.e., h is the density of (n − P)−1/2 times the square root of a chi-square distributed random variable with n − P degrees of freedom. In view of Proposition 3.1 and Theorem 5.3.22 in Gaenssler and Stute (1977), we may evaluate the conditional probabilities in (21) by fixing

at the value s and then by computing the unconditional probabilities. With B shorthand for the event {|Tp*| ≥ scp,|Tp+1*| < scp+1,…,|TP*| < scP} this gives
where we have made use of independence of

from (Tp+1*,…,TP*) and also of the mutual independence of the variables Tj* (cf. Proposition 3.1). Observe that on the far r.h.s. of (22) the first factor of the integrand in the numerator is identical to the numerator in the expression for Fn,θ,σ*(t|p) given in (10), except for the fact that the critical value cp has been replaced by scp. Replacing this factor in (22) by the equivalent expression given in (11) with scp taking now the place of cp, using Fubini's theorem and making use of (16) one can immediately read off the density of Fn,θ,σ(t|p):

where
Formula (23) shows that fn,θ,σ(t|p) is the multivariate normal density φn,p(t) times a “modification factor” mn,p,θ,σ that is only a function of tp. Whereas the corresponding modification factor for fn,θ,σ*(t|p) was seen in (12) to be an indicator function (divided by a normalizing constant) leading to an excised normal distribution, the modification factor (24) is of a more complicated nature; in particular, the indicator function (and thus the excision interval) is “smoothed” through integration with respect to (w.r.t.) the distribution of

. The modification factor mn,p,θ,σ(tp) is zero at tp = −n1/2μn,p(p), is symmetric about that point, and strictly increases to unity as the argument tp moves away from −n1/2μn,p(p). Also note that fn,θ,σ(·|p) is symmetric about zero if μn,p(p) = 0, which arises, e.g., if p > p0(θ). Furthermore, if μn,j(j) = 0 for p ≤ j ≤ P, which is the case if p > p0(θ) holds, the conditional density fn,θ,σ(·|p) is independent of θ.
As a point of interest we note that, contrary to the known-variance case, (22), (23), and (24) show a dependence on the tests based on Tp+1,…,TP. However, this dependence can be seen to fade out with increasing sample size (cf. Leeb and Pötscher, 2000, Remark 6.3(ii)).
The unconditional finite-sample distribution of the post-model-selection estimator

can now easily be expressed in terms of the conditional distributions Fn,θ,σ(·|p) and the selection probabilities

. Note that the selection probabilities πn,θ,σ(p) for p ≥ 1 are precisely given by the denominator in (24) (or (22)); for p = 0 this formula also gives πn,θ,σ(0) if we use the convention that the first factor in these integrals is set equal to 1. Furthermore, note that the selection probabilities are all positive for each n. Let

with u ∈ RP denote the unconditional c.d.f.. Using (18) and (20) we obtain

where we use the convention that Fn,θ,σ(·|0) ≡ 1. Using (22), (23), and (24), (26) can be written as
with the convention that the integral w.r.t. r in (27) is to be interpreted as 1 when p = 0. Similarly as with (12) and (24), the c.d.f. given in (27) can be viewed as a “smoothed” version of (17) through integration w.r.t. the distribution of

. As in the case of (17), the c.d.f. given by (27) can be used for the computation of moments or coverage probabilities.
In the previous section the finite-sample distributions of the post-model-selection estimator

and of its idealized version

conditional on selecting a model of order p have been obtained. In the known-variance case the resulting formulas are quite simple and easy to interpret, but this is not so in the unknown-variance case (compare (12) with (23) and (24)). In the latter case one could thus think of achieving simplification by passing to the large-sample limit. Assuming that X′X/n converges to a positive definite matrix Q, the results in Pötscher (1991) imply that in case p ≥ p0(θ) and p > 0 the conditional finite-sample distribution of

defined in (20) (and (9)) converges to a limiting distribution F∞,θ,σ(·|p), the density of which is given by

if p > p0(θ), i.e., if θ ∈ Mp−1, and by

if p = p0(θ), i.e., if θ ∈ Mp[setmn ]Mp−1. Here ξ∞,p is the limit of ξn,p as n → ∞ and the normal density φ∞,p(t) has been defined in Section 2. The asymptotic distribution given by f∞,θ,σ(·|p) in (28) and (29) is certainly simpler than the conditional finite-sample distribution of

given by fn,θ,σ(·|p) in (23) and (24). To gain insight into the accuracy of f∞,θ,σ(·|p) as an approximation to fn,θ,σ(·|p), we first compare f∞,θ,σ(·|p) with the conditional finite-sample density fn,θ,σ*(·|p) of the idealized version

. As discussed after (13), in case p > p0(θ), i.e., θ ∈ Mp−1, the asymptotic distribution (28) is identical to its finite-sample counterpart given by (13), except that X [p]′X [p]/n and ξn,p have been replaced by their respective limits; furthermore, (13) is independent of θ. As a consequence, the accuracy of (28) as an approximation to (13) is only governed by the speed of convergence of X′X/n to its limit Q and, in particular, is uniform over all θ ∈ Mp−1. In case p = p0(θ), i.e., θ ∈ Mp[setmn ]Mp−1, the asymptotic expression in (29) is somewhat simpler than (12) but at the expense of missing an essential feature of the finite-sample distribution, namely, the interval of excision in (12). The reason for this is that in case p = p0(θ) the center of the excision interval

, which diverges to ±∞ (regardless of how small θp is), whereas the interval's width stays bounded. Thus the excision interval “disappears” at ±∞ in the limit. (Note that in contrast the excision interval is centered at zero in case p > p0(θ).) As a consequence, the asymptotic distribution (29) will poorly approximate the corresponding conditional finite-sample distribution of

in case θp is of order

. In particular, convergence of the corresponding c.d.f.s is not uniform w.r.t. θ ∈ Mp[setmn ]Mp−1 (cf. Corollary 4.6, which follows). (See also Pötscher, 1991, Remark 4(iii); and the related discussion in Kabaila, 1995; and Pötscher, 1995.) Both phenomena just discussed, namely, uniformity over Mp−1 in the convergence to the asymptotic distribution and nonuniformity over Mp[setmn ]Mp−1, can also be expected to occur for

instead of

because the conditional finite-sample distribution of

is essentially a “smoothed” version of the corresponding distribution of

(cf. (23) and (24) and the attending discussion). This expectation is confirmed by the theoretical results obtained subsequently (cf. (34) and (35) and Corollary 4.6). It is also in agreement with the results of a simulation study reported in Pötscher and Novak (1998), which showed that the conditional finite-sample distribution Fn,θ,σ(·|p) of

is reasonably well approximated by its asymptotic counterpart in case p > p0(θ), i.e., θ ∈ Mp−1, whereas this approximation can be quite poor if p = p0(θ), i.e., if θ ∈ Mp[setmn ]Mp−1.
The just discussed “nonuniformity” defect of the asymptotic distribution as an approximation to the conditional finite-sample distribution of

may prompt one to look for alternative (asymptotic) approximations that retain the same level of simplicity as the asymptotic distribution without suffering from its defects. It turns out that such asymptotic approximations can indeed be found if we allow these approximating distributions to depend—contrary to (28) and (29)—on sample size. In fact, the distributions given by fn,θ,σ*(·|p) in (12) turn out to be the appropriate approximations. They are as simple and easy to interpret as f∞,θ,σ(·|p) given in (28) and (29), but they will be shown in Theorem 4.2 to approximate the finite-sample distributions given by fn,θ,σ(·|p) in (23) and (24) uniformly over (suitable large subsets of) the parameter space. In particular, the unpleasant restriction p ≥ p0(θ), i.e., θ ∈ Mp, underlying the asymptotic results in Pötscher (1991) can be removed entirely in the linear model framework considered in the present paper. As a by-product, we then also obtain in Corollary 4.5 the limiting conditional distribution even for the case p < p0(θ), i.e., θ ∉ Mp.
We first recall a few facts about distances between distribution functions F and G on Rp. The total variation distance is given by

where the sup is taken over all Borel sets A in Rp. Certainly, supt∈Rp|F(t) − G(t)| ≤ ∥F − G∥TV holds, and hence convergence in total variation distance implies convergence in the sup-norm, which in turn implies weak convergence. If λ is a dominating (σ-finite) measure for F and G (which always exists), then

, where f and g are the densities of F and G w.r.t. λ. As a consequence, convergence in total variation distance is equivalent to convergence of the corresponding density functions in the L1-sense. In the following we shall only be concerned with the case where the dominating measure λ is Lebesgue measure. The L1-distance between f and g w.r.t. Lebesgue measure will be denoted by ∥ f − g∥1.
The following preliminary result is instrumental in allowing the transfer of results (such as the uniformity/nonuniformity phenomena discussed previously) from the known-variance case to the unknown-variance case.
PROPOSITION 4.1. For every p, 1 ≤ p ≤ P, we have

for n → ∞. As a consequence,

for n → ∞.
As argued in the introduction to this section, the conditional distribution of

is close to its asymptotic counterpart uniformly for θ ∈ Mp−1. In fact, it is easy to see that

and hence

for n → ∞.5
Subject to θ ∈ Mp−1, the densities fn,θ,σ*(·|p) and f∞,θ,σ(·|p) do in fact not depend on θ; furthermore, it is easy to see that the L1-distance in (32) is independent of σ (cf. (13) and (28)). Result (32) now follows from λ-a.e. pointwise (in t) convergence and Scheffé's theorem. (Cf. also the proof of Proposition 4.3.)

and hence

for n → ∞. Similarly, the nonuniformity in the closeness of the conditional distribution of

and its asymptotic counterpart when θ varies in Mp[setmn ]Mp−1, outlined in the introduction to this section, can be transferred to the unknown-variance case by means of Proposition 4.1. For a precise statement see Corollary 4.6, which follows.
A further important implication of Proposition 4.1 is that fn,θ,σ*(·|p) provides a better approximation to fn,θ,σ(·|p) than the asymptotic distribution given by (28) and (29) in that (30) holds uniformly for θ ∈ Mp, whereas (34) holds only uniformly for θ ∈ Mp−1. Despite its usefulness, Proposition 4.1 suffers from the limitation that θ is confined to Mp, and hence this result does not tell us anything about closeness of fn,θ,σ*(·|p) and fn,θ,σ(·|p) if the true value of θ falls outside of Mp, i.e., if p0(θ) > p. It would therefore be advantageous to have available a similar result but without any restriction on p0(θ) and, in particular, without confining θ to Mp. This is indeed possible at the expense of a more difficult proof.
THEOREM 4.2. For every p, 1 ≤ p ≤ P, any bounded subset C of RP, and any positive constant σ* > 0 we have

for n → ∞. As a consequence,

for n → ∞. The preceding conclusions remain valid more generally for any set C that is contained in a set of the form Rp × D, where D can be any bounded subset of RP−p.6
In case p = P, this condition allows for all subsets C ⊆ RP including C = RP.
The significance of the preceding theorem is to establish that the easily interpretable formula (12) for fn,θ,σ*(·|p) indeed provides a uniform (w.r.t. θ, σ) approximation to (23) and (24), the conditional density of the post-model-selection estimator

, over large subsets of the entire parameter space.
7The restriction on C in Theorem 4.2 is of no real significance and in particular implies local uniformity. Perhaps it could be removed by another method of proof. In this context we note that this restriction can indeed be avoided for the corresponding result concerning the unconditional distributions (cf. Theorem 5.2).
The limiting conditional distributions of the post-model-selection estimator

and of its idealized version

will be obtained next for all values of p and not only under the restriction p ≥ p0(θ) as in Pötscher (1991). Such a complete description of the limiting behavior of the conditional distributions in the linear model framework also rests on Theorem 4.2. (We repeat, however, that the limiting conditional distributions do not provide a uniform approximation to the finite-sample distributions over the complement of Mp−1 [cf. Corollary 4.6].) The stepping-stone to the results in this section is the following proposition.
PROPOSITION 4.3. Let p satisfy 1 ≤ p ≤ P and let θ(n) ∈ RP be a sequence such that n1/2μn,p(p) converges to a limit νp ∈ R ∪ {−∞,∞}, where μn(p) is defined by (6) with θ(n) replacing θ. Furthermore, let σ(n) be a sequence of positive real numbers with (finite) limit σ > 0 and recall that ξ∞,p is the large-sample limit of ξn,p. Then we have the following results.
(a) The conditional density fn,θ(n),σ(n)*(t|p) converges to the density

for λ-almost all t ∈ Rp and hence in the L1-sense. (Note that (36) reduces to the normal density φ∞,p in (29) in case νp = ±∞ and to (28) in case νp = 0.) Consequently, the conditional c.d.f. Fn,θ(n),σ(n)*(·|p) converges to the c.d.f. with density (36) in the total variation distance.
(b) If, additionally, θ(n) is bounded, also the conditional density fn,θ(n),σ(n)(t|p) converges to (36) in the L1-sense, and hence the conditional c.d.f. Fn,θ(n),σ(n)(·|p) converges to the c.d.f. with density (36) in the total variation distance.
We note that (36) is an excised normal density, i.e., (36) is the density of P(U ≤ t,|Up + νp| ≥ σξ∞,p cp)/P(|Up + νp| ≥ σξ∞,p cp) where U is a p × 1 random vector with c.d.f. Φ∞,p.
Remark 4.4.
(i) If n1/2μn,p(p) does not converge, Proposition 4.3 can be applied to subsequences of θ(n) along which n1/2μn,p(p) converges. Because R ∪ {−∞,∞} is compact, and hence every subsequence contains a convergent subsequence, Proposition 4.3 in fact shows for any sequence θ(n) that every accumulation point of the sequence fn,θ(n),σ(n)*(·|p) w.r.t. the L1-distance necessarily is of the form (36) (i.e., any accumulation point of the sequence Fn,θ(n),σ(n)*(·|p) w.r.t. the total variation distance has a density of the form (36)). The same holds for fn,θ(n),σ(n)(·|p) and Fn,θ(n),σ(n)(·|p) provided the sequence θ(n) is bounded.
(ii) Inspection of the proof shows that the boundedness assumption on θ(n) in part (b) of Proposition 4.3 can be weakened to boundedness of θ(n)[¬p] . The latter condition is, e.g., trivially satisfied if θ(n) ∈ Mp for all n.
The limiting conditional distributions of the post-model-selection estimator

and of its idealized version

under fixed parameter and also local alternatives asymptotics now follow easily. In the following Q = limn→∞ X′X/n is partitioned as

where Q[p : p] is of dimension p × p.
COROLLARY 4.5. Let p satisfy; 1 ≤ p ≤ P. For θ ∈ RP consider the local alternatives given by

where γ ∈ RP. Let σ(n) be a sequence of positive real numbers converging to σ, 0 < σ < ∞.
(a) Suppose θ ∈ Mp−1 is satisfied, i.e., p > p0(θ) holds. Then fn,θ(n),σ(n)(·|p) and fn,θ(n),σ(n)*(·|p) both converge to (36) in the L1-sense, where

That is, the conditional c.d.f.s Fn,θ(n),σ(n)(·|p) and Fn,θ(n),σ(n)*(·|p) converge to an excised normal distribution, namely, to the c.d.f. of (36), in the total variation distance (and hence uniformly in t ∈ Rp).
(b) Suppose θ ∈ Mp[setmn ]Mp−1 is satisfied, i.e., p = p0(θ) holds. Then fn,θ(n),σ(n)(·|p) and fn,θ(n),σ(n)*(·|p) both converge to the normal density φ∞,p in the L1-sense. That is, the conditional c.d.f.s Fn,θ(n),σ(n)(·|p) and Fn,θ(n),σ(n)*(·|p) converge to the normal c.d.f. Φ∞,p in the total variation distance (and hence uniformly in t ∈ Rp).
(c) Suppose θ ∈ RP[setmn ]Mp is satisfied, i.e., p < p0(θ) holds. Suppose

is nonzero (which is the case for all θ except for the elements of a hyperplane). Then fn,θ(n),σ(n)(·|p) and fn,θ(n),σ(n)*(·|p) both converge to the normal density φ∞,p in the L1-sense. That is, the conditional c.d.f.s Fn,θ(n),σ(n)(·|p) and Fn,θ(n),σ(n)*(·|p) converge to the normal c.d.f. Φ∞,p in the total variation distance (and hence uniformly in t ∈ Rp).
The limiting density function obtained in Corollary 4.5 will be denoted by f∞,θ,σ,γ(·|p) and the corresponding c.d.f. by F∞,θ,σ,γ(·|p). In case γ = 0 we shall write f∞,θ,σ(·|p) and F∞,θ,σ(·|p) as shorthand for f∞,θ,σ,0(·|p) and F∞,θ,σ,0(·|p). Note that Corollary 4.5 only ensures well-definedness of f∞,θ,σ,γ(·|p) and F∞,θ,σ,γ(·|p) for all θ ∈ Mp and also for those θ ∈ RP[setmn ]Mp that make (38) nonzero.
In case γ = 0 (i.e., fixed parameter asymptotics), parts (a) and (b) of Corollary 4.5 reproduce the asymptotic distributions given in (28) and (29), which were obtained from the results in Pötscher (1991).8
The convergence results for the conditional c.d.f.s in Pötscher (1991) are formulated in terms of pointwise convergence. Because the limiting conditional c.d.f.s are continuous (when viewed on the appropriate subspace), convergence of the c.d.f.s in the sup-norm (taken over the appropriate subspace) then follows automatically from Polya's theorem (cf. Billingsley and Topsoe, 1967, Ex. 6; Chandra, 1989). The results in Pötscher (1991) do not, however, imply convergence w.r.t. total variation distance.
Corollary 4.5 (and Proposition 4.3) shows that the limiting behavior of the distribution of the post-model-selection estimator

, conditional on having selected model order p, is mainly governed by the behavior of

given by (6) with θ(n) replacing θ. In discussing the implications of the preceding corollary, we consider first the case θ ∈ Mp corresponding to parts (a) and (b). For simplicity of presentation, assume also that γ ∈ Mp, i.e., γ[¬p] = 0.
9This assumption is rather innocuous, as the general case γ ∈ RP is completely similar.

then reduces to

, and one immediately sees that it is the pth component of

that determines whether the limiting distribution is a normal (if θp ≠ 0) or an excised normal distribution (if θp = 0). This dichotomy is exactly the same as in the case of fixed parameter asymptotics, but now in case of an excised normal distribution the center of excision is not necessarily zero but is given by −γp. As discussed earlier, the shape of the finite-sample distribution of

, conditional on having selected model order p, will—in case the true parameter value in Mp is close to but outside of Mp−1—be badly captured by the shape of the limiting conditional distribution obtained from fixed parameter asymptotics with θ(n) ≡ θ ∈ Mp[setmn ]Mp−1, regardless of how close θ is to Mp−1. However, if this case is modeled in a local alternatives framework by taking the true parameter value θ(n) to satisfy θ(n) ∈ Mp[setmn ]Mp−1 with θ(n) approaching

, then the limiting conditional distribution will better capture the essential features of the finite-sample distribution by predicting an excised normal distribution rather than a normal distribution.
We next turn to the case θ ∉ Mp corresponding to part (c) of Corollary 4.5. Observe that

is given by
If the expression in (38) is nonzero,

tends to ±∞, resulting in a limiting normal distribution. Otherwise (without additional assumptions on the regressors),

can show all kinds of limiting behavior, including oscillatory behavior, in which case no limit for Fn,θ(n),σ(n)(·|p) and Fn,θ(n),σ(n)*(·|p) exists. Of course, along convergent subsequences of

the limiting distribution follows from Proposition 4.3 and will be an excised normal distribution or a normal distribution, depending on whether the limit of the subsequence of

is finite or ±∞ (cf. Remark 4.4(i)).
We conclude this section with a formal statement of the nonuniformity phenomenon in the convergence of the conditional finite-sample distributions to their limits. As a starting point, recall that the conditional finite-sample densities fn,θ,σ*(·|p) and fn,θ,σ(·|p) converge to their limit f∞,θ,σ(·|p) in the L1-sense uniformly in θ and σ if θ varies in Mp−1 only and σ > 0 (cf. (32)–(35)). However, in contrast to the results given in Proposition 4.1 and Theorem 4.2, uniformity in the convergence to the limiting density f∞,θ,σ(·|p) (or to the c.d.f. F∞,θ,σ(·|p)) need not hold when θ varies in Mp or in bounded subsets of the entire parameter space. In fact, uniformity already breaks down locally near Mp−1.
COROLLARY 4.6. Let p satisfy 1 ≤ p ≤ P. For every t ∈ Rp and every σ > 0 there exists a positive ρ ∈ R such that for every θ ∈ Mp−1

where

denotes the ball

. Consequently,

The same is also true if Fn,θ,σ(·|p) and fn,θ,σ(·|p) are replaced by Fn,θ,σ*(·|p) and fn,θ,σ*(·|p), respectively.
Corollary 4.6 shows in particular that convergence to the limiting distribution is not uniform over tubes in Mp that surround Mp−1. It can be shown that uniformity in fact holds in the complement (relative to Mp) of any such tube (of fixed positive radius).10
More precisely, for every σ > 0 and every ρ > 0 we have supθ∈Mp,|θp|>ρ∥ fn,θ,σ(·|p) − f∞,θ,σ(·|p)∥1 → 0 for n → ∞, and the same holds with fn,θ,σ*(·|p) replacing fn,θ,σ(·|p).
It is easy to see that the nonuniformity near Mp−1 typically also arises when approaching Mp−1 from within RP[setmn ]Mp. Furthermore, outside of Mp additional nonuniformity can arise near the hyperplane mentioned in Corollary 4.5(c). Again, outside a tube of fixed positive radius surrounding this hyperplane convergence is uniform (at least over bounded subsets of the complement of such a tube).
In this section we study the asymptotic properties of the unconditional distribution functions of the post-model-selection estimator

and of its idealized version

and obtain results paralleling those in Section 4. In particular, we find again that the limiting distribution does not provide a uniform approximation to the unconditional finite-sample distributions Gn,θ,σ(u) and Gn,θ,σ*(u) (cf. Corollary 5.5). Also, uniform closeness of Gn,θ,σ(u) and Gn,θ,σ*(u) can again be established (see Theorem 5.2). Analogous results for the selection probabilities πn,θ,σ(p) and πn,θ,σ*(p) defined in Section 3 are also obtained.
Because the c.d.f.s Gn,θ,σ and Gn,θ,σ*, respectively, can be linearly expressed in terms of Fn,θ,σ(t|p)πn,θ,σ(p) and Fn,θ,σ*(t|p)πn,θ,σ*(p) (cf. (26) and (14)), a key step for the results in this section is the following lemma.
LEMMA 5.1. For every p, 1 ≤ p ≤ P, we have

for n → ∞. As a consequence,

for n → ∞.
The following results parallel Theorem 4.2.
THEOREM 5.2.
(a) For the unconditional distribution functions we have

and hence

for n → ∞.
(b) Let p satisfy 0 ≤ p ≤ P. The selection probabilities satisfy

for n → ∞.
In contrast to Theorem 4.2, we do not need to restrict θ to a set C or to require σ to satisfy σ ≥ σ* > 0 when taking the suprema in (42). These restrictions arose in the proof of Theorem 4.2 from the need to control the behavior of ratios of probabilities that vanish asymptotically. In the unconditional case considered in Theorem 5.2 this difficulty does not arise, allowing us to avoid these restrictions. We also note that the c.d.f.s Gn,θ,σ and Gn,θ,σ* do not have densities w.r.t. Lebesgue measure on RP, because both distributions put positive mass on every subspace M0,…,MP. For this reason, (42) is given in terms of total variation distance between distribution functions rather than in terms of the L1-distance between density functions.12
Of course, (42) could be expressed in terms of the L1-distance between density functions w.r.t. a dominating (σ-finite) measure, which, however, now cannot be Lebesgue measure.
We next consider the limit of the unconditional distributions of the post-model-selection estimator

and of its idealized version

. The following proposition contains the main technical step.
PROPOSITION 5.3. Let p satisfy 0 ≤ p ≤ P and let θ(n) ∈ RP be a sequence such that n1/2μn,j(j) converges to a limit νj ∈ R ∪ {−∞,∞} for j = max(1,p),…,P, where μn(j) is defined by (6) with θ(n) replacing θ. Furthermore, let σ(n) be a sequence of positive real numbers with (finite) limit σ > 0. Then:
(a) If p ≥ 1, the quantity fn,θ(n),σ(n)*(t|p)πn,θ(n),σ(n)*(p) converges to

for λ-almost all t ∈ Rp and hence in the L1-sense. Furthermore, fn,θ(n),σ(n)(t|p)πn,θ(n),σ(n)(p) also converges to (43) in the L1-sense. (In case νp = ±∞ the indicator function in (43) is to be interpreted as the constant 1.) As a consequence, Fn,θ(n),σ(n)*(·|p)πn,θ(n),σ(n)*(p) and Fn,θ(n),σ(n)(·|p)πn,θ(n),σ(n)(p) converge to the distribution with density (43) in the total variation distance (and hence uniformly in t ∈ Rp).13
The total variation distance for distribution functions with finite mass (not necessarily equal to one) is defined exactly as in the case where total mass is one. In this more general context the inequality supt|F(t) − G(t)| ≤ ∥F − G∥TV ≤ ∫| f − g|dλ still holds, where f and g, respectively, denote densities of F and G w.r.t. a dominating (σ-finite) measure λ.
(b) The selection probabilities πn,θ(n),σ(n)*(p) and πn,θ(n),σ(n)(p) converge to

where we use the convention that in case p = 0 the first factor in (44) is set equal to one. (Note that (43) and (44) are zero whenever |νj| = ∞ for some j satisfying p + 1 ≤ j ≤ P.)
(c) If |νj| = ∞ for some j satisfying p ≤ j ≤ P, then πn,θ(n),σ(n)*(r) and πn,θ(n),σ(n)(r) converge to zero for 0 ≤ r < p.
We note that the subsequence argument given in Remark 4.4(i) applies to Proposition 5.3 also. With the help of Proposition 5.3 we can now obtain the unconditional asymptotic distribution under fixed and local alternatives asymptotics.
COROLLARY 5.4. For θ ∈ RP consider the local alternatives given by

where γ ∈ RP and let σ(n) be a sequence of positive real numbers with (finite) limit σ > 0.
(a) For 0 ≤ p ≤ P, the selection probabilities πn,θ(n),σ(n)(p) and πn,θ(n),σ(n)*(p) converge to π∞,θ,σ,γ(p), which is given by

with

(b) The unconditional finite-sample distributions Gn,θ(n),σ(n) and Gn,θ(n),σ(n)* converge to a c.d.f. G∞,θ,σ,γ in the total variation distance (and hence uniformly in u ∈ RP). The limit G∞,θ,σ,γ satisfies

where F∞,θ,σ,γ(·|p) was introduced after Corollary 4.5 for p ≥ 1 and is set equal to 1 for p = 0.
The limiting distribution (47) is a convex combination of excised and nonexcised normal distributions concentrated on subspaces of different dimensions. In contrast to the unconditional finite-sample distribution (cf. (14) and (26)), however, only terms with p ≥ p0(θ) enter into the limiting distribution as a result of the fact that the selection probabilities for models with p < p0(θ) converge to zero.14
For this reason the limit G∞,θ,σ,γ is well defined for all θ ∈ RP, because F∞,θ,σ,γ(·|p) is well defined on a set containing all θ satisfying p ≥ p0(θ).
In case γ = 0 (i.e., fixed parameter asymptotics), the limiting distribution in Corollary 5.4 reduces to the limiting distribution one obtains by applying the results in Pötscher (1991) to the linear model considered here. We shall write G∞,θ,σ and π∞,θ,σ(p), respectively, for G∞,θ,σ,0 and π∞,θ,σ,0(p). In case γ = 0, the formula for the limiting distribution simplifies to
with the convention that the first integral on the far r.h.s of (48) is set equal to 1 if p0(θ) = 0. The asymptotic selection probabilities also simplify to

. Note that the (excised) normal distributions in (48) are now all symmetric about zero and that the asymptotic selection probabilities depend only on the critical values cj (cf. Pötscher, 1991, Lemma 4).
As in the conditional case discussed in Section 4, the convergence of the unconditional finite-sample distribution to its limit is not uniform w.r.t. θ. Heuristically speaking, there are two sources for this nonuniformity. The first source is the nonuniformity in the convergence of the conditional distributions (Corollary 4.6), which spills over into the unconditional distribution. The second is the nonuniformity in the convergence of the selection probabilities (established in Corollary 5.6, which follows) taken together with the fact that the limiting distribution (48) does not contain terms with p < p0(θ).
COROLLARY 5.5. For every u ∈ RP and every σ > 0 there exists a positive ρ ∈ R such that for every θ ∈ MP−1
The same is also true if Gn,θ,σ is replaced by Gn,θ,σ*.
Corollary 5.5 shows in particular that convergence to the limiting distribution is not uniform over tubes surrounding MP−1. It can be shown that uniformity in fact holds in the complement of any such tube (of fixed positive radius).15
More precisely, for every σ > 0 and every ρ > 0 we have supθ∈RP,|θP|>ρ∥Gn,θ,σ − G∞,θ,σ∥TV → 0 for n → ∞, and the same holds with Gn,θ,σ* replacing Gn,θ,σ.
One could furthermore ask if results similar to (32)–(35) hold, i.e., if Gn,θ,σ converges to G∞,θ,σ (either in total variation distance or for every u ∈ RP) uniformly over MP−1 (or over a smaller set Mr, r > 0). As Gn,θ,σ is a convex combination of all the conditional distributions Fn,θ,σ(·|p), it should again not come as a surprise that the answer is no because by an argument similar to the proof of Corollary 5.5, the following more general result can be established: let q(u) = min{i : 0 ≤ i ≤ P,ui+1 > 0,…,uP > 0} and set q(u) = P if the set over which the minimum is taken is empty. Then (49) holds with

replaced by any of the smaller sets

for any r satisfying max{p0(θ) + 1,q(u)} ≤ r ≤ P.
We finally turn to a discussion of uniformity and nonuniformity in the convergence of the selection probabilities to their limits. If θ ∈ Mp−1, 1 ≤ p ≤ P, we have μn,j(j) = 0 for j ≥ p, and hence πn,θ,σ*(p) given by (15) and (16) coincides with π∞,θ,σ(p) given by (45) with γ = 0. Consequently,

holds for 1 ≤ p ≤ P, and an application of Theorem 5.2 gives

as n → ∞ for 1 ≤ p ≤ P. In the next result we describe regions of nonuniformity in the convergence of the selection probabilities to their limits.
COROLLARY 5.6.
(a) Let p satisfy 1 ≤ p ≤ P. Then for any positive ρ ∈ R, any σ > 0, and any θ ∈ Mp−1

where

was defined in Corollary 4.6.
(b) Let p satisfy 0 ≤ p < P. Then for any positive ρ ∈ R, any σ > 0, and any θ ∈ Mp we have

Parts (a) and (b) also hold with πn,θ,σ(p) replaced by πn,θ,σ*(p).
Corollary 5.6(a) shows, in particular, that convergence of the selection probabilities πn,θ,σ(p) and πn,θ,σ*(p) to their limiting value is not uniform over tubes in Mp that surround Mp−1. It can be shown that over the complement (w.r.t. Mp) of any such tube of fixed positive radius the convergence is in fact uniform. These results parallel the results for the conditional distributions given in Corollary 4.6 and in the attending discussion. In contrast to the results for the conditional distributions, however, Corollary 5.6(b) furthermore shows that nonuniformity in the convergence of πn,θ,σ(p) and πn,θ,σ*(p) also arises near any point in Mp. Again, outside of any tube (in RP) of fixed radius surrounding Mp convergence is uniform as can be shown.
Remark 6.1. In defining the conditional finite-sample distributions Fn,θ,σ*(·|p) and Fn,θ,σ(·|p), the estimator has been centered at μn(p), the expected value of the restricted least-squares estimator given in (6). For the majority of the results (e.g., for the finite-sample results in Section 3, Proposition 4.1, and Theorem 4.2 and also for the analogous results in Section 5) the particular choice of centering constants is in fact inessential (cf. Leeb and Pötscher, 2000, Remark 6.1). The effects of different choices of centering constants on the remaining results are discussed in Remarks 6.1 and 6.2 of Leeb and Pötscher (2000).
Remark 6.2.
(i) The model selection procedures considered in this paper are based on a sequence of tests that use critical values cj that do not depend on sample size and satisfy 0 < cj < ∞ for 1 ≤ j ≤ P. If the critical values (for 1 ≤ j ≤ P) are allowed to depend on sample size, the finite-sample results trivially remain valid without any change. The asymptotic results all remain valid if the sample-size-dependent critical values, say, cn,j, satisfy cn,j → c∞,j for n → ∞ with 0 < c∞,j < ∞ (and if c∞,j replaces cj in the formulas for the limiting p.d.f.s, c.d.f.s, and selection probabilities). In fact, the asymptotic results not involving the limiting c.d.f. or p.d.f. such as Proposition 4.1, Theorem 4.2, Lemma 5.1, and Theorem 5.2 even hold if 0 < lim inf cn,j ≤ lim sup cn,j < ∞ is satisfied.
(ii) The assumption that X′X/n → Q > 0, used for the asymptotic results in Sections 4 and 5, can be weakened to 0 < lim inf λmin(X′X/n) ≤ lim sup λmax(X′X/n) < ∞ for all asymptotic results that do not involve the limiting c.d.f. or p.d.f.. (The results involving the limiting distribution of course also hold under this weaker condition along subsequences for which X′X/n converges.) Furthermore, Proposition 4.1, Lemma 5.1, and Theorem 5.2 in fact even hold without any condition on the asymptotic behavior of X′X/n.
Remark 6.3.
(i) The results of this paper readily adapt to situations where a subvector of θ is assumed to be common to all candidate models, i.e., where there is a p[bull ] > 0 such that only models from the list Mp[bull ],…,MP should be selected. First observe that setting cp[bull ] = 0 forces the model selectors

to do precisely this, i.e., makes them satisfy

. Second, with max(p0(θ),p[bull ]) now playing the rôle of p0(θ), one immediately sees that the conditional finite-sample distributions for p > p[bull ] are the same as in the case p[bull ] = 0 discussed in Section 3 and that now fn,θ,σ*(·|p[bull ]) = fn,θ,σ(·|p[bull ]) = φn,p[bull ](·), a density that does not depend on θ at all. As a consequence, all results concerning conditional distributions continue to hold for p > p[bull ] and become trivial in case p = p[bull ]. The results for the unconditional distributions and the selection probabilities also continue to hold with obvious, mainly notational, changes. See Leeb and Pötscher (2001) for more discussion.
(ii) The finite-sample results in Section 3 adapted to the situation discussed in (i) substantially generalize the results of Giles and Srivastava (1993), who consider a regression model yt = α + βxt + εt with only one regressor. Giles and Srivastava (1993) obtain the unconditional finite-sample distribution of the post-model-selection estimator for α, when model selection is based on a t-test for the hypothesis β = 0. Elsinger (1994) generalizes their result to the model yt = x1,t′α + x2,t′ β + εt and obtains the unconditional finite-sample distribution of the post-model-selection estimator for the vector α when model selection is based on an F-test for the hypothesis that the vector β satisfies β = 0.
Remark 6.4.
(i) For the construction of the test statistics Tp the estimator

obtained from fitting the overall model MP has been used rather than an estimator that is obtained from fitting model Mp. Such a choice is reasonable from a practical point of view, because it avoids overestimation of the error variance when model Mp is not true, which obviously has adverse effects on the test.
(ii) The finite-sample results in Section 3 are obviously tied very strongly to the assumptions of the paper (linear model, normality, choice of

. Also some of the asymptotic results such as, e.g., Theorem 4.2, rely heavily on these assumptions, and it is not obvious to which extent they can be generalized, whereas other asymptotic results should be more amenable to generalization. These and related questions are currently under investigation.
The finite-sample distributions of the post-model-selection estimator

derived in Section 3 are quite complicated and difficult to interpret. Insight into the behavior of these distributions can, however, be gained through a simple and easy to interpret uniform approximation that is provided in the paper. This approximation is superior to the asymptotic distribution, which is known to provide an inadequate approximation to the finite-sample distribution under certain circumstances. As a by-product, the uniform approximation result also allows the completion of the analysis in Pötscher (1991), in that the asymptotic distribution of the post-model-selection estimator

conditional on selecting an incorrect model is obtained. We note that the uniform approximation and the asymptotic distribution both depend on the unknown parameter value θ and hence cannot be used directly for purposes of inference. Consistent estimators for the finite-sample distribution of the post-model-selection estimator

can be obtained based on the results of the present paper. Such estimators are discussed in detail in Leeb and Pötscher (2001), where it is shown that such estimators cannot be uniformly consistent.
The proof of Proposition 3.1 rests on the following lemma, which establishes uncorrelatedness of certain random variables of key interest. The result is hardly new, and variants of it are folklore. Note that we do not assume a true regression relationship to hold in this lemma.
LEMMA A.1. Let Z be an n × 1 random vector whose components are uncorrelated and have constant variance. Let W be a nonstochastic n × k matrix of full column rank and let

be the ordinary least-squares estimator obtained from regressing Z on W. Let W = [W1 : W2] and let

be partitioned conformably, with W1 being of dimension n × k1, where 0 < k1 < k. Let

be the ordinary least-squares estimator obtained from regressing Z on W1 only. Then both

are uncorrelated with

. Furthermore,

are uncorrelated.
Proof. The first claim is simply verified by calculating the appropriate covariances. To prove the second claim, let PW1⊥ = (In − W1(W1′W1)−1W1′) be the projection on the orthogonal complement of the column space of W1 and define W° = [W1 : V] , where V = PW1⊥W2. Let

denote the ordinary least-squares estimator obtained from regressing Z on W°. Clearly,

are uncorrelated. Note that

Multiplying this identity by PW1⊥ from the left yields

Because V has full column rank, we obtain

. Observing that

completes the proof. █
Proof of Proposition 3.1. Repeated application of Lemma A.1 implies mutual uncorrelatedness of

. (In case p = 0, observe that

.) In view of the Gaussianity assumption the preceding list of random variables is in fact independent. By definitions (3)–(5), the proposition is then a simple consequence of this independence result. █
LEMMA B.1. Let rm, m ≥ 1, and sm, m ≥ 1, be sequences of nonnegative real numbers such that rm − sm and rm sm converge to ∞. Then

for m → ∞.
Proof. Without loss of generality we may assume that rm − sm is positive for each m. Define ψ(x) = φ(x)/x, where φ is the standard normal density. Then we may write

From Gradstejn and Ryzik (1985, equation (8.254), p. 931) or Feller (1966, Lemma VII.1.2), we obtain for x > 0 that 1 − Φ(x) = ψ(x)(1 − R(x)) where |R(x)| ≤ x−2. This implies

Furthermore,

which completes the proof. █
LEMMA B.2. Let Wm be a nonnegative random variable such that mWm2 is chi-square distributed with m degrees of freedom, m ≥ 1, and let ε ≥ 0. Then

Proof. The case ε = 0 is trivial; hence assume ε > 0. Using the moment generating function of the chi-square distribution and Markov's inequality we obtain for any 0 < t < ½

Setting t(ε) = ½(2ε + ε2)/(1 + ε)2 we see that 0 < t(ε) < ½ and h(t(ε),ε) = (ε(2 + ε) − 2 log(1 + ε))/2. Because log(1 + ε) < ε, we have h(t(ε),ε) > (ε(2 + ε) − 2ε)/2 = ε2/2. █
LEMMA B.3. Let Wm, m ≥ 1, be as in the previous lemma and let τi,m, m ≥ 1, be a sequence of nonnegative real numbers for i = 1,…,l. Assume that the sequence τi,m converges to some τi ∈ R ∪ {∞} for m → ∞ and that τi,m = O(m1/2) for each i = 1,…,l. Assume that τi = ∞ for i = 1,…,k where 1 ≤ k ≤ l and that τi ∈ R for i = k + 1,…,l. Define τ*,m = min{τ1,m,…,τk,m}. Let di, i = 1,…,l, be positive real numbers and 0 < ε < 1. Then there exists a real number K such that for every α satisfying 0 < α < min{1/d1,…,1/dk}
holds. The constant K depends only on k, di, i = 1,…,k, and the sequences τi,m, i = 1,…,k, whereas the constant implicit in the O(·) notation may depend on all sequences τi,m, all di, ε, and even on α.
Proof. Because Δ(a,b) is strictly increasing in b, and because Δ(a,b) ≤ 1, the ratio in (B.1) is bounded from above by

Observe that the expectation in the denominator of (B.2) converges to

by dominated convergence because Wm → 1 in probability. Hence, we can find a constant K(1) such that (B.2) is bounded from above by

Observe that τi,m − diατ*,m → ∞ for i = 1,…,k, because diα < 1, and that τi,m, 1 ≤ i ≤ k, is positive for sufficiently large m. Hence, Lemma B.1 implies that there exists a positive constant K(2) such that (B.3) is bounded from above (for sufficiently large m) by
where

and ψ is as in the proof of Lemma B.1. Observe that 1 − di(1 − ε)/τi,m → 1 and that |1 − diατ*,m /τi,m| ≥ 1 − diα > 0 for i = 1,…,k. Hence, for sufficiently large m, we can find a positive constant K(4) such that (B.4) is bounded from above by

Because τi,m = O(m1/2) by assumption, we can find a positive constant L depending only on the di's and the sequences τi,m, i = 1,…,k, such that 0 ≤ diτi,mτ*,m /m ≤ L holds. Setting K = kL, (B.5) is seen to be bounded by

Application of Lemma B.2 completes the proof. █
For the remainder of this Appendix let Z be a standard normally distributed random variable that is independent of Wm for every m ≥ 1, where Wm is as in Lemma B.2. Define

and

where τi,m, i = 0,…,l, l ≥ 0, are real numbers and 0 < di < ∞, i = 0,…,l, holds. (If l = 0, the product in (B.6) is to be interpreted as unity.)
LEMMA B.4. Assume that τi,m ∈ R converges to τi ∈ R ∪ {−∞,∞} for m → ∞, i = 0,…,l, and that τi,m = O(m1/2) for each i = 1,…,l. Then

Proof. Without loss of generality we may assume that all elements τi,m are nonnegative. Introduce the random variables

with the convention that Am = 1 in case l = 0. We then observe that

Because fm* = (1 − Δ(τ0,m,d0))−1 on the event {|Z − τ0,m| ≥ d0} and because τ0,m → τ0 ∈ R ∪ {∞} implies Δ(τ0,m,d0) → Δ(τ0,d0), the lemma is proved if we can establish that

Because Δ(·,·) is continuous on (R ∪ {−∞,∞}) × R, convergence in probability of Δ(τi,m,Wm di) to Δ(τi,di) follows from Wm → 1 in probability. Because Δ(·,·) is bounded, it follows that EAm converges to

whereas EBm converges to

. In case τ1,…,τl are all finite or l = 0, it is easy to see that the limit of EBm is positive, and hence (B.7) immediately follows in this case.
In case at least one τi, i = 1,…,l, is infinite, the limits of both EAm and EBm are zero, and a more delicate argument is needed to establish (B.7): Without loss of generality we may assume that τi = ∞ for i = 1,…,k, 1 ≤ k ≤ l, and that τi is finite for i = k + 1,…,l. Set τ*,m = min{τ1,m,…,τk,m}. For arbitrary but fixed 0 < ε < 1, write

where

where α satisfies 0 < α < min{1/d1,…,1/dk}. We first show that EAm(1)/EBm → 0:
because Wm → 1 in probability and Δ(τ0,(1 + ε)d0) < 1. Second, observe that

Next we show that EAm(i)/EBm → 0 for i = 3,4. Because EAm(2)/EBm is bounded as shown in (B.8), it suffices to establish EAm(i)/EAm(2) → 0, i = 3,4. Lemma B.3 implies that EAm(3)/EAm(2) = O(exp(−m(ε2/2 − Kα))), where K is a constant independent of α. Choosing α sufficiently small establishes convergence to zero of EAm(3)/EAm(2). Turning to EAm(4)/EAm(2) observe that

where we have first made use of Δ(a,b) ≤ 1 and then of monotonicity of Δ(·,·) in its second argument. Because τi is finite for i = k + 1,…,l, the limit of

is positive. To prove convergence to zero of EAm(4)/EAm(2) it hence suffices to establish that

converges to zero for m → ∞. By Lemmas B.1 and B.2 the expression in (B.10) is bounded by a constant times

Because τi,m = O(m1/2) and because τ*,m → ∞ by construction, it follows that the expression in (B.11), and hence the upper bound in (B.9), converges to zero.
Taking these results together we have now established that

Because the r.h.s. of (B.12) converges to the r.h.s. of (B.7) for ε → 0, the proof is complete. █
LEMMA B.5. Assume that τi,m ∈ R converges to τi ∈ R ∪ {−∞,∞} for m → ∞, i = 0,…,l, and that τi,m = O(m1/2) for i = 1,…,l. Then

Proof. Without loss of generality we may assume that all elements τi,m are nonnegative. Because fm* is identically zero on the event {|Z − τ0,m| < d0} and because fm ≥ 0, it suffices to show that E(fm1{|Z − τ0,m| < d0}) converges to zero. Observe that

where Am and Bm have been defined in the proof of Lemma B.4.
Note that 1{d0Wm ≤ |Z − τ0,m| < d0} converges to zero in probability because using independence of Z and Wm we have that
and the upper bound in (B.14) converges to zero because Wm → 1 in probability and because Δ(·,·) is continuous and bounded. As shown in the proof of Lemma B.4, the random variables Am and Bm converge in probability to nonzero constants in the case where all τ1,…,τl are finite or l = 0. Because Am and Bm are bounded, it follows that (B.13) converges to zero in this case.
Next consider the case when at least one τi for i = 1,…,l is infinite. Without loss of generality assume that the first k of these τi are infinite whereas the remaining l − k are finite. Using arguments identical to the ones leading to (B.14) we may write the numerator of (B.13) as
where Am(1) and Am(2) have been defined in the proof of Lemma B.4. In that proof, it was also shown that EAm(1)/EBm → 0 and lim supm→∞ EAm(2)/EBm ≤ (1 − Δ(τ0,(1 + ε)d0))−1 for m → ∞. It follows that the lim sup of (B.13) is bounded by

for every 0 < ε < 1. Letting ε → 0 completes the proof. █
Consider a sequence θ(n) ∈ RP and a sequence σ(n) of positive real numbers. For p satisfying 1 ≤ p ≤ P we will need to express

in a different form. Define τj,n = −n1/2μn,j(j)σ(n)−1ξn,j−1 for j = p,…,P, where μn(j) is given by (6) with θ replaced by θ(n). Observe that fn,θ(n),σ(n)*(·|p) and fn,θ(n),σ(n)(·|p) both are a product of φn,p(·) (with σ(n) replacing σ) times a function that depends on tp but not on t1,…,tp−1. Decomposing φn,p(t) (with σ(n) replacing σ) into the product of the marginal density of the last component and the conditional density of the first p − 1 coordinates given the last one, the p-fold integral representing the L1-norm in (C.1) can easily be reduced to
where we have used the representations of fn,θ(n),σ(n)*(·|p) and fn,θ(n),σ(n)(·|p) given in (12), (23), and (24), respectively, and where U(n)(p,scp) denotes U(p,scp) after replacement of σ by σ(n). Furthermore, φ(·;(σ(n))2ξn,p2) denotes the density of a normally distributed random variable with mean zero and variance (σ(n))2ξn,p2. Performing the substitution r = σ(n)−1ξn,p−1tp this can be rewritten as
The following probabilistic reinterpretation of (C.2) will prove useful. Let Z be a standard normally distributed random variable and let Wn for n > P be a nonnegative random variable, such that (n − P)Wn2 is chi-square distributed with n − P degrees of freedom. Furthermore Z and Wn are assumed to be independent for every n > P. Define random variables fn and fn* by
and
where E(·) denotes the expectation operator w.r.t. the joint distribution of Z and {Wn : n > P}. It is now easy to see that (C.2), and hence (C.1), is equal to

Observe that Efn = Efn* = 1 holds in view of the definition of Δ(·,·) and independence of Z and Wn. Consequently,

and therefore

Proof of Proposition 4.1. It suffices to show for every given p, 1 ≤ p ≤ P, that (C.1), and hence (C.3), converges to zero for n → ∞ for any sequence θ(n) ∈ Mp and σ(n) > 0. Because θ(n) ∈ Mp, it follows that μn,j(j) = 0 for j = p + 1,…,P and hence τj,n = 0 for j = p + 1,…,P. To verify convergence of (C.3) to zero, it suffices to show that every subsequence (ni) contains a further subsequence (ni(k)) such that the convergence occurs along this subsequence (ni(k)). Because R ∪ {−∞,∞} is compact, every subsequence contains a further subsequence along which τp,n converges to some τp ∈ R ∪ {−∞,∞}. Hence, for verifying convergence of (C.3) we may assume without loss of generality that τp,n converges to τp. Set τj = 0 for j = p + 1,…,P. Decompose the expectation on the r.h.s of (C.3) as follows:

Upon making the identification m = n − P, l = P − p, τi,m = τi+p,m+P, τi = τi+p, Wm = Wm+P, fm* = fm+P*, fm = fm+P, di = ci+p for i = 0,…,l, and noting that τi,m = 0 for i = 1,…,l, an application of Lemmas B.4 and B.5 establishes that (C.3) converges to zero. █
Proof of Theorem 4.2. Again it suffices to show for every given p, 1 ≤ p ≤ P, that (C.3) converges to zero for n → ∞, where now θ(n) is any sequence in C and σ(n) ∈ R satisfies σ(n) ≥ σ* > 0. By a reasoning similar to that in the proof of Proposition 4.1, we may assume without loss of generality that τj,n converges to some τj ∈ R ∪ {−∞,∞} for every j = p,…,P. For any sequence θ(n) ∈ C the sequence θ(n)[¬p] is bounded because of the assumptions on C maintained in the theorem. Observe that μn,j(j) for j = p + 1,…,P depends on θ(n) only through θ(n)[¬p] . Hence, boundedness of μn,j(j) for j = p + 1,…,P follows because X′X/n → Q > 0. Because ξn,j converges to a positive constant and because σ(n) ≥ σ* > 0, the relation τj,n = O(n1/2) for j = p + 1,…,P follows. Decomposing (C.3) as in the proof of Proposition 4.1, we may again apply Lemmas B.4 and B.5 to conclude convergence to zero of (C.3). █
As a point of interest we note the following: the proof of Proposition 4.1 makes use of Lemmas B.4 and B.5. However, as shown in the proof, τi,m = 0 for i = 1,…,l holds as a result of the assumption θ(n) ∈ Mp, and thus this corresponds to the trivial case discussed in the proofs of Lemmas B.4 and B.5. As a consequence, the proof of Proposition 4.1 does not rely on Lemmas B.1–B.3 at all. However, these lemmas and also the full complexity of the proofs of Lemmas B.4 and B.5 are required for the proof of Theorem 4.2, because of the fact that the case θ(n) ∉ Mp (implying the presence of unbounded τi,m) is possible under the assumptions of this theorem.
Proof of Proposition 4.3.
(a) In view of (12), the conditional density fn,θ(n),σ(n)*(t|p) is the product of a centered normal density with variance-covariance matrix σ(n)2(X [p]′X [p]/n)−1 times an indicator function and a normalizing factor. Pointwise convergence of the normal density to φ∞,p is obvious because the variance-covariance matrix corresponding to the former density converges to the variance-covariance matrix corresponding to the latter density. The arguments of the Δ(·,·)-function appearing in the normalizing factor converge to the arguments of the Δ(·,·)-function in (36). By continuity of Δ(·,·) on (R ∪ {−∞,∞}) × R, the normalizing factor converges to the normalizing factor in (36). The endpoints of the excision interval that defines the indicator function converge to the endpoints of the excision interval of (36) under the assumptions of the proposition. Hence the indicator function appearing in the formula for fn,θ(n),σ(n)*(t|p) converges to the one in (36) at least for all tp not equal to the endpoints of the excision interval in (36). Because the set of all t ∈ Rp such that the last coordinate is equal to a given value is obviously a Lebesgue null set, the λ-almost sure convergence of fn,θ(n),σ(n)*(t|p) to (36) follows. Convergence in the L1-norm then follows from Scheffé's theorem.
(b) This follows immediately from part (a) and Theorem 4.2. █
Proof of Corollary 4.5. In light of Proposition 4.3 it only remains to show that the limit νp of

satisfies (37) under the assumptions of part (a) and equals ±∞ under the assumptions of parts (b) and (c). Note that

, defined by (6) with θ(n) replacing θ, is given by (39). Under the assumptions of part (a) we have θ[¬p] = 0 and θp = 0, which shows that νp is indeed given by (37). For part (b) note that θp ≠ 0, whereas θ[¬p] = 0. This implies divergence of

to νp = ∞ or νp = −∞ in this case. Part (c) follows because condition (38) again implies divergence of

. █
Proof of Corollary 4.6. We first prove (40) with Fn,θ,σ(t|p) replaced by Fn,θ,σ*(t|p). For given t ∈ Rp and σ > 0 choose α ≠ 0 smaller than −tp − σξ∞,p cp and let ρ be a real number larger than |α|. For any given θ ∈ Mp−1, define

where e(p) is the pth standard basis vector in RP. By Corollary 4.5(a) the c.d.f. Fn,θ(n),σ*(·|p) converges to the c.d.f. of an excised normal distribution with density (36), where νp = α. By definition of α we have tp < −α − σξ∞,p cp, the lower endpoint of the excision interval in (36). Consequently, Fn,θ(n),σ*(t|p) converges to Φ∞,p(t)(1 − Δ(−ασ−1ξ∞,p−1,cp))−1. Because θ(n) ∈ Mp[setmn ]Mp−1, it follows from Corollary 4.5(b) that F∞,θ(n),σ(t|p) = Φ∞,p(t). This implies

as n → ∞. Because ασ−1ξ∞,p−1 is finite and cp is positive, we see that the limit in (C.4) is positive. Observing that

because |α| < ρ, the result (40) with Fn,θ,σ*(·|p) replacing Fn,θ,σ(·|p) follows. Proposition 4.1 then immediately delivers (40). █
Proof of Lemma 5.1. To prove the lemma it suffices to show for every 1 ≤ p ≤ P that

for n → ∞ for any sequence θ(n) ∈ RP and any sequence of positive real numbers σ(n). Arguing similarly as at the beginning of Appendix C, it is easy to see that the L1-norm in (D.1) can be written as

where τj,n has been defined in Appendix C. With random variables Z and Wn as in Appendix C, the expression in (D.2) can be rewritten as

The expression in (D.3) is bounded from above by

Using a similar subsequence argument as in the proof of Theorem 4.2, we may assume without loss of generality that τj,n converges to a limit τj ∈ R ∪ {−∞,∞} for all j. Recalling that Wn → 1 in probability and that Z and Wn are independent, it is easy to see that both indicator functions in (D.4) converge to the same limit 1{|Z − τp| ≥ cp} in probability, where the latter indicator function is to be interpreted as the constant 1 in case τp = ±∞. Because Δ(·,·) is continuous on (R ∪ {−∞,∞}) × R, convergence of the expression inside the expectation operator in (D.4) follows. Convergence of (D.4) to zero now follows from the dominated convergence theorem, because the integrand in (D.4) is bounded by 2. █
Proof of Theorem 5.2. We prove part (b) first. It suffices to show for every 0 ≤ p ≤ P that

for n → ∞ for any sequence θ(n) ∈ RP and any sequence of positive real numbers σ(n). Arguing as in the proof of Lemma 5.1 we may assume that τj,n converges to a limit τj ∈ R ∪ {−∞,∞} for all j. It is easy to see that the absolute value in (D.5) can be rewritten as
in case p ≥ 1 and as

in case p = 0. Because Wn → 1 in probability, because Δ(·,·) is continuous on (R ∪ {−∞,∞}) × R and is bounded, convergence of (D.6) and (D.7) to zero for n → ∞ follows immediately. This completes the proof of part (b).
To prove part (a) observe that, using (14), (26), and the triangle inequality, the total variation distance between Gn,θ,σ and Gn,θ,σ* can be bounded from above by the sum over p = 0,…,P of

By our conventions, this reduces to |πn,θ,σ(0) − πn,θ,σ*(0)| in case p = 0, which goes to zero uniformly in θ and σ as already shown. For p ≥ 1 observe that a translation of the argument of the distribution function does not affect the total variation distance and that the c.d.f.s in (D.8) are both concentrated on the same subspace. It is then easy to see that (D.8) is bounded from above by the L1-distance between fn,θ,σ(·|p)πn,θ,σ(p) and fn,θ,σ*(·|p)πn,θ,σ*(p) w.r.t. the Lebesgue measure on that subspace. An application of Lemma 5.1 then completes the proof. █
Proof of Proposition 5.3. We prove parts (b) and (c) first. Because Δ(·,·) is continuous on (R ∪ {−∞,∞}) × R, convergence of Δ(−n1/2μn,j(j)σ(n)−1ξn,j−1,cj) to Δ(−νjσ−1ξ∞,j−1,cj) for j = max(1,p),…,P follows immediately. Parts (b) and (c) for πn,θ(n),σ(n)*(p) now follow from (15) and (16), observing for part (c) that under the assumptions of this part at least one factor in (15) converges to zero and the others are bounded by one. Applying Theorem 5.2(b) delivers parts (b) and (c) also for πn,θ(n),σ(n)(p). Part (a) for fn,θ(n),σ(n)*(·|p)πn,θ(n),σ(n)*(p) now follows from part (b) and Proposition 4.3(a). An application of Lemma 5.1 then completes the proof of the proposition. █
LEMMA D.1. Let Hn be a sequence of distribution functions of finite mass (not necessarily equal to one) on Rk, which converges to H in total variation distance. Let an ∈ Rk be a sequence with limit a ∈ Rk. Assume that Hn and H are absolutely continuous w.r.t. Lebesgue measure and that the density h of H is continuous almost everywhere. Then Hn(· + an) converges to H(· + a) in the total variation distance.
Proof. Observe that

It hence suffices to show that H(· + an) converges to H(· + a) in the total variation distance. Because the density h is continuous almost everywhere, the density h(· + an) of H(· + an) converges almost everywhere to the density h(· + a) of H(· + a). Convergence of h(· + an) to h(· + a) in the L1-sense now follows from Scheffé's theorem. The proof is completed by observing that ∥H(· + an) − H(· + a)∥TV ≤ ∥h(· + an) − h(· + a)∥1. █
Proof of Corollary 5.4. For θ(n) as in the corollary and 1 ≤ j ≤ P recall that

is given by (39) with j replacing p. Because θj and θ[¬j] are zero for j > p0(θ), one immediately sees that

converges to υj given in (46) for j > p0(θ). If p0(θ) > 0, then for j = p0(θ) one also sees that

converges to νj = ±∞, because θj ≠ 0 and θ[¬j] = 0. Hence the assumptions of Proposition 5.3 are satisfied for any p ≥ p0(θ). Part (a) of the corollary is now an immediate consequence of Proposition 5.3(b). To prove part (b), expand Gn,θ(n),σ(n)* as in (14) and observe that the terms for p < p0(θ) converge to zero in total variation distance because the probabilities πn,θ(n),σ(n)*(p) vanish in the limit as shown in part (a) and because the conditional c.d.f.s have total mass one. For p ≥ p0(θ) observe that

converges to −(Q[p : p])−1Q[p : ¬p]γ[¬p] and that

. Part (b) for Gn,θ(n),σ(n)* then follows from an application of Proposition 5.3 together with Lemma D.1. (Observe that for the calculation of the total variation distance between corresponding terms of Gn,θ(n),σ(n)* and G∞,θ,σ,γ, the indicator functions appearing in these corresponding terms are identical and can be ignored.) The analogous result for Gn,θ(n),σ(n) now follows from Theorem 5.2(a). █
Proof of Corollary 5.5. We first prove (49) with Gn,θ,σ* replacing Gn,θ,σ. For given u ∈ RP and σ > 0 choose α ≠ 0 such that

holds. Let ρ be a real number larger than |α| and set

where e(P) is the Pth standard basis vector in RP. Note that

. Because θ ∈ MP−1 and α ≠ 0, it follows that p0(θ(n)) = P. Hence,

in view of Corollaries 4.5 and 5.4. On the other hand, Gn,θ(n),σ*(u) converges to G∞,θ,σ,αe(P)(u) given by (47) with γ = αe(P). Because uP + α < 0, the indicator functions in (47) are zero for p < P, and hence G∞,θ,σ,αe(P)(u) reduces to

in view of Corollaries 4.5(a) and 5.4(a). Because of (D.9), the upper integration limit uP in (D.11) is larger than the left endpoint of the excision interval. Hence the expressions in (D.10) and (D.11) differ, showing that the limits of G∞,θ(n),σ(u) and Gn,θ(n),σ*(u) are different. This proves the result for Gn,θ,σ*. The result for Gn,θ,σ now follows from Theorem 5.2(a). █
Proof of Corollary 5.6.
(a) Let p satisfy 1 ≤ p ≤ P, let ρ > 0 and σ > 0 be arbitrary, and choose an arbitrary θ ∈ Mp−1. Define

with 0 < |α| < ρ and where e(p) denotes the pth standard basis vector in RP. Observe that θ(n) ∈ Mp[setmn ]Mp−1 and that

. Now, (45) (with γ = 0) implies

because p0(θ(n)) = p in view of α ≠ 0. Corollary 5.4 (with γ = αe(p)) implies

for n → ∞. It follows that |πn,θ(n),σ*(p) − π∞,θ(n),σ(p)| converges to a positive constant.
(b) For p satisfying 0 ≤ p < P and arbitrary ρ > 0, σ > 0, and θ ∈ Mp define

, where 0 < |α| < ρ. Observe that θ(n) ∈ Mp+1[setmn ]Mp and that

. Applying (45) (with γ = 0) implies

because p0(θ(n)) = p + 1 > p. If p0(θ) = p, Corollary 5.4 (with γ = αe(p+1)) implies

because υp+1 = α and υj = 0 for j > p + 1; if p0(θ) < p, Corollary 5.4 implies πn,θ(n),σ*(p) → (1 − Δ(−υpσ−1ξ∞,p−1,cp))A where υp = α((Q[p : p])−1× Q[p : ¬p]e(p+1)[¬p])p. It follows that |πn,θ(n),σ*(p) − π∞,θ(n),σ(p)| converges to a positive constant.
The preceding results prove the corollary for πn,θ,σ*(p). The result for πn,θ,σ(p) now follows from an application of Theorem 5.2(b). █