The Decisions and Ideal Points of British Law Lords

Chris Hanretty

doi:10.1017/S0007123412000270

The Decisions and Ideal Points of British Law Lords

Published online by Cambridge University Press: 24 September 2012

Chris Hanretty

Article contents

Abstract
Why Might Judges Judge Politically?
Data and Model
Results
Discussion
Footnotes

Rights & Permissions

Abstract

Policy-sensitive models of judicial behaviour, whether attitudinal or strategic, have largely passed Britain by. This article argues that this neglect has been benign, because explanations of judicial decisions in terms of the positions of individual judges fare poorly in the British case. To support this argument, the non-unanimous opinions of British Law Lords between 1969 and 2009 are analysed. A hierarchical item-response model of individual judges’ votes is estimated in order to identify judges’ locations along a one-dimensional policy space. Such a model is found to be no better than a null model that predicts that every judge will vote with the majority with the same probability. Locations generated by the model do not represent judges’ political attitudes, only their propensity to dissent. Consequently, judges’ individual votes should not be used to describe them in political terms.

Information

Type: Articles
Information: British Journal of Political Science , Volume 43 , Issue 3 , July 2013, pp. 703 - 716
DOI: https://doi.org/10.1017/S0007123412000270 [Opens in a new window]
Copyright: Copyright © Cambridge University Press 2012

In November 2001, Home Secretary David Blunkett implied that judges who objected to plans to indefinitely detain foreign nationals suspected of terrorism lived in an ‘airy fairy libertarian’ world.Footnote ¹ Those measures had been struck down by the Appellate Committee of the House of Lords (the ‘Law Lords’) by a majority of eight to one.Footnote ² One interpretation of that decision is that it split eight airy-fairy libertarians from one hard-nosed realist – that is, it separated judges located in a dimension running from libertarianism to conservatism.

Analysing non-unanimous decisions in order to estimate the locations of judges in the political space is commonplace in political science. Scholars have shown that US Supreme Court Justice Ginsburg is more liberal than Justice Scalia,Footnote ³ that Australian High Court Justice Kirby is to the left of Justice CallinanFootnote ⁴ and that Canadian Supreme Court Justice L'Heureux-Dubé is to the left of Justice Sopinski.Footnote ⁵ Despite David Robertson's work on judicial discretion in the Lords,Footnote ⁶ it is not clear whether we have comparable grounds for believing, say, that Lord Scarman is to the left of Baron Ackner.

This article argues that we cannot locate Law Lords in the political space on the basis of their individual votes. Whilst we can recover ideal points for judges, an ideal point model is a very poor model of judges’ decision making, and should be rejected. Even if the model were accepted, the ideal points do not represent positions in the political space, but rather judges’ attitudes towards dissent. Consequently, it is mistaken to call judges ‘airy fairy libertarians’, ministerial comments notwithstanding.

Why Might Judges Judge Politically?

There is an extensive literature on the politics of the judiciary. We know that, definitionally, courts are political institutions,Footnote ⁷ that they have important consequences for the rest of the political systemFootnote ⁸ and that judges can play important non-judicial roles in public life.Footnote ⁹ My focus is narrower. When I describe judges as being political, or talk of judges judging politically, I mean that they make decisions on the basis of ‘political’ beliefs: specifically, that when judges decide how to dispose of a case – typically whether to allow or dismiss an appeal – their decisions are a function of the location of that case and that judge in some political space, such that judges who are far apart in that political space will be less likely to agree on the disposition of a case. This definition encompasses both ‘attitudinal’Footnote ¹⁰ and ‘strategic’Footnote ¹¹ accounts of political judging, but excludes analyses that try to explain the decisions of panels of judges or infer judges’ positions from the decisions of panels they have sat on.Footnote ¹²

There are both general and particular reasons for believing that judges are political in this sense. Generally, judges in comparable courts have been shown to be political. Of the seven common law courts of last resort in large, consolidated democracies, analysis of judges’ ideal points has been undertaken in four courts: the US and Canadian Supreme Courts, the Australian High Court, and, for a limited period, the Appellate Committee itself.Footnote ¹³ Scholars who have analysed these courts have always provided estimates of judges’ political positions – even if, in certain cases, the solutions provided were ‘not technically very good’.Footnote ¹⁴ Consequently, if the Law Lords do not judge politically, they would be an exception to a general pattern amongst similarly located bodies.

The particular reason for believing that we can locate judges in the political space is that British politicians and commentators have often described judges as holding certain political values, and implied or stated that these values influence their decisions. Judges have been variously – and contradictorily – described as pursuing ‘the protection of property rights, and… political views normally associated with the Conservative party’Footnote ¹⁵; having ‘the ideology of old-middle class men… [and] the ethos of those who run an administrative state’Footnote ¹⁶, and as being ‘airy fairy libertarians’. Often, these values have been ascribed to the judiciary as a whole. This characterization might mean that judges who share the same values always reach the same decision, and that analysing dissenting opinions is useless. However, this view has always been rather difficult to square with the brute fact of dissent. As Lee asks:Footnote ¹⁷

How can it be so simple when there is a 3-2 split in the House of Lords, overturning a 0-3 decision in the Court of Appeal, which was itself overturning the High Court?

Consequently, the attribution to judges en masse of certain political values gives us reason to believe that individual judges judge politically in the sense described above.

Existing quantitative studies of Appellate Committee decision making also suggest that judges judge politically. Early work by David RobertsonFootnote ¹⁸ used multidimensional scaling (MDS) to analyse non-unanimous Appellate Committee decisions between 1965 and 1978. He found that three dimensions characterized judicial behaviour. The first dimension concerned criminal law, with high scores associated with finding for the prosecution. The second dimension concerned public law, with high scores associated with finding for the state. The third dimension was left uninterpreted. Even with three dimensions, the fit of the MDS solution was poor, with high stress values.

Later work by Robertson abandoned MDS, and with it the analysis of (dis)agreement between judges. Judicial Discretion in the House of Lords exploited the fact that cases are heard by panels of the Appellate Committee, and that consequently judges may hear some cases but not others. Robertson conducted multiple discriminant analysis on cases heard between 1986 and 1995, asking, for a number of particular outcomes of interest – findings for the Revenue in tax cases, for the state in public law cases, for plaintiffs in constitutional law and civil liberties cases, and for the defendant in criminal cases – whether the (assumed random) presence of judge X on the panel made such an outcome more or less likely. In order to combine insights from different types of cases, factor analysis was performed on judges’ scores on the linear discriminant analysis.

Although a number of factor analytic solutions were possible, Robertson's preferred solution involved dropping criminal cases and presenting two dimensions: egalitarianism (associated with finding for the state in public law and for the plaintiff in civil liberties cases) and constitutionalism (finding for the plaintiff in constitutional cases). Because this method of analysis can use unanimous decisions, Robertson was able to make inferences on the basis of far more cases than would have been possible including only cases with dissent – though at the cost of specifying, ex ante, the components of judicial ideology.

At the same time, there are considerable grounds for doubting that British judges judge politically. The first is that levels of dissent are limited in comparative perspective, and whilst unanimity may point to the homogeneity of judicial preferences or the absence of Dworkinesque ‘tough cases’, it may also indicate that judges do not decide on the basis of their political positions, but rather on the basis of shared views of what the law requires. That is, agreement may indicate that judges are not political. Figure 1 shows that agreement in the House of Lords is higher than agreement in all those common law courts of last resort in which analysis of dissenting opinions has been successfully applied.Footnote ¹⁹ Only judges on the Indian Supreme Court agree more, and they face a much higher caseload.

Fig. 1

Agreement rates across five courts

Second, the British constitution offers few opportunities for policy-seeking judges. Attitudinal models of judicial decision making, in which judges’ political attitudes are the exclusive determinants of judicial behaviour, have been assumed to apply best where courts are at the top of their respective judicial hierarchy, and are not subject to overrule. Yet for most of the period discussed here, British courts have been at risk of legislative overrule by simple majorities. Whilst strategic decision making – that is, decision making in anticipation of legislative overrule – has not been thought severe enough to entirely preclude the estimation of judges’ political locations, the constraint implied by legislative overrule by simple majority is so extensive, and the policy ‘core’ so reduced, that a strategic desire to avoid overrule may cause British judges to become political mutes, reducing them to redundant veto points. Consequently, ‘political’ judges in the British system would have to act with casual disregard for the possibility of overrule – and, one might reason, be unlikely to reach the higher rungs of the judiciary in the first place.

Data and Model

I use data from the High Courts Judicial Database,Footnote ²⁰ which includes data on all decisions that were heard between 1969 and 2003 by the Appellate Committee of the House of Lords (or by the Privy Council acting in its judicial capacity) and reported in the All England Law Reports. I have supplemented this data with my own data on all non-unanimous cases decided by the Appellate Committee between 2004 and 2009.

I consider only non-unanimous cases – those in which there was at least one dissenting opinion – in this article.Footnote ²¹ By a dissenting opinion, I mean an opinion that disagreed with the majority of the court over how to dispose of the case: typically, though not exclusively, whether to allow or to dismiss the appeal. I do not, therefore, consider opinions that disagree with the majority of the court over the ratio decidendi of the case.Footnote ²²

The data matrix is therefore made up of 1,592 individual decisions taken by fifty-nine judges in 318 cases. Decisions by a small number of judges who heard very few casesFootnote ²³ were excluded. My data also contain information on the outcome of each case. These outcomes have, in certain areas of the law, been coded as ‘liberal’ or ‘conservative’, following established usage.Footnote ²⁴ Table 1 shows this information, and the number of cases in seven broad areas of the law. Information about case outcomes is used in the model that I now describe.

Table 1

Areas of the Law and Outcomes

Note: Percentages in ‘liberal’ and ‘conservative’ columns do not sum to 100% because not all cases had a clear direction.

To explain judicial decisions I use a hierarchical item response model estimated using Bayesian methods. Item response models have become increasingly popular in political science, and can be considered to directly operationalize the attitudinal model of judicial decision making. They improve on previous methods of analysing judicial behaviour, in particular multidimensional scaling of agreement between judges, by relaxing the assumption that every instance of (dis)agreement between judges is related to the latent trait under investigation. Bayesian methods – in particular the Markov Chain Monte Carlo (MCMC) method – allow otherwise intractable or computationally expensive models to be estimated.Footnote ²⁵

The response I wish to model is the ‘vote’ y of each judge j in a given case i. By convention, y_ij = 1 if the judge voted with the majority, and y_ij = 0 if the judge dissented. The probability of voting with the majority can be modelled as a function of three variables: the judge's location and the location and discrimination of the case. The judge's location ( $$\[-->$<>\theta<$> <!--$$ _j) is his/her location in an n-dimensional political space. In this note, the policy space is one-dimensional, and the presumption is that the dimension will run from left to right, or from liberal to conservative.

The case discrimination parameter (β_i) represents the degree to which the case discriminates with respect to the recovered dimension: cases with higher absolute values of β_i are very good at separating judges along the recovered dimension. This parameter also tells us which end of the policy space is more likely to vote with the majority. If the space is indeed a left-right policy space, a case with a positive discrimination parameter requires ‘more’ of the latent trait (positions further along the real number line to the right) to vote with the majority – and therefore has a right-leaning outcome. Conversely, a case with a negative discrimination parameter implies a left-leaning outcome. The case location parameter (α_i) represents how much of the latent trait is needed to vote with the majority – that is, how far along the recovered dimension the case discriminates.

I link these variables to each judge's vote as follows:Footnote ²⁶

$$Pr({{Y}_{ij}}\, = \,1)\, = \,\phi ({{\beta }_i}{{\theta }_j}\:{\rm{ - }}\:{{\alpha }_i}),$$

where φ(·) is the cumulative normal distribution.

I innovate in my treatment of the case discrimination parameter. There are three broad approaches to dealing with discrimination parameters.Footnote ²⁷ One approach is to set the value of the discrimination parameter to one for all cases. This is the simplest operationalization of the spatial voting model. Models with fixed discrimination parameters are common in the educational testing literature, where they are referred to as Rasch models.Footnote ²⁸ Constraining the discrimination parameter in this way makes sense in educational testing, since investigators may reasonably presume that standardized test items tap an underlying dimension to the same degree and in a similar way. The same is not true of legislative roll calls or court cases, which may discriminate with respect to the recovered dimension to various degrees, with some strongly discriminating, others weakly discriminating and others not discriminating at all.

A second approach is to sample the discrimination parameters from an uninformative prior distribution. Where investigators have reason to believe that items differ in discriminating between positions on the recovered dimension, and where no auxiliary information concerning the contents of the items is available, this is the best approach. The downside of this approach is that it does not employ auxiliary information concerning the substantive content of the items, therefore model parameters may be highly uncertain.

A third approach is to sample some or all of the discrimination parameters from an informative prior distribution. In most instances, this method has involved constraining some discrimination parameters to take on theoretically informed values. Bafumi et al. consider, but ultimately reject, constraining the discrimination parameters for a model of US Supreme Court voting in which ‘1’ indicates ‘liberal’ outcomes: such an approach ‘relies too strongly on the precoding, which, even if it is generally reasonable, is not perfect’.Footnote ²⁹ Jackman sets two roll calls that are mirror images of each other to discriminate, with equal and opposite strength, with respect to the second recovered dimension in a multidimensional item response model.Footnote ³⁰

Both of these strategies use auxiliary information to estimate item response models with genuinely informative parameter estimates. They rely, however, on the choice of the discrimination parameters to constrain.

A more forgiving strategy is to model the discrimination parameters as a function of other variables. Here, I model the discrimination parameters as a function of the broad area of law and of the direction of the outcome, considered either as a ‘liberal’ or ‘conservative’ outcome. The discrimination parameters are drawn from normal distributions, the means of which are modelled as a linear function of these area-specific intercepts and the direction of the case outcome. Thus, if x_i =1 denotes a ‘liberal’ outcome in case i, and k indexes the seven areas of law shown in Table 1, the discrimination parameters can be modelled as follows:

$${{\beta }_i}\, \sim \,N(({{\gamma }_{0k}}\, + \,{{\gamma }_{1k}}{{x}_i}),\sigma ),$$

where γ ₀_k and γ ₁_k are area-specific intercepts and coefficients, respectively.Footnote ³¹ Cases without directionality are drawn from an uninformative prior distribution.

This strategy allows us to plausibly exploit information about the area and the outcome. Suppose, as Robertson claimed, that tax cases discriminate between judges very well, with some judges favouring the Inland Revenue and others favouring taxpayers. In that case, the area-specific intercept will be close to zero and the parameter attached to the case outcome will not only be very large, but if the recovered dimension runs from ‘left’ to ‘right’, will also be strongly negative. If, by contrast, family law cases do not on average discriminate with respect to the recovered dimension, the parameter attached to the case outcome will not be different from zero.

I estimated this model using the JAGS MCMC sampler. The model was identified by post-processing the MCMC output so that (1) ideal points had mean zero and unit standard deviation and (2) Bridge of Harwich was to the right of Griffiths.Footnote ³² The code used is shown in the online appendix. The model was run for two million iterations, discarding the first 750,000 iterations as burn-in and thinning the remaining samples by a factor of 250. A standard convergence diagnostic (Geweke's diagnostic) and inspection of the trace plots showed no problems with convergence.Footnote ³³

Results

Whilst the model does produce estimates of judges’ locations, which show differences between judges (see Figure 2), this article argues that the model that produces these estimates should not be accepted – and that these estimates do not, in any case, represent a substantive dimension of politics. I base this argument on three points: first, the fit of the model is extremely poor, and does not represent an improvement over a null model; secondly, the parameters relating to case discrimination do not make sense; and thirdly, whilst the locations might seem at first glance to indicate strong partisan differences between judges, these locations do not reflect judges’ political attitudes, but rather their attitudes to dissent.

Fig. 2

Judge locations

First, I discuss model fit. I take as my comparison a null model in which every judge votes with the majority with p = 0.695, equal to the percentage of concurring opinions in the dataset. Table 2 presents a number of indicators of fit for both the null model and the item response model.

Table 2

Model Fit Statistics

Note: ‘Discriminating cases’ are those cases that had a discrimination parameter whose 95 per cent credible interval did not encompass zero.

It is clear from the table that the item response model scarcely improves on the null model. Considering the four different measures of model fit – the percentage of decisions predicted correctly, the log-likelihood, the average percentage reduction in error (APRE)Footnote ³⁴ and the geometric mean probability (GMP)Footnote ³⁵ – the item response model outperforms the null model only by very small amounts. This extremely limited improvement, when coupled with the considerable cost in terms of the number of model parameters compared to the null model, ought to discourage us from adopting the model.

Secondly, the discrimination parameters, and the coefficients that predict them, do not make sense if the recovered dimension is to run from left to right. We should expect cases with a liberal outcome to have negative discrimination parameters, and cases with a conservative outcome to have positive ones. Yet all ‘liberal’ cases had a positive discrimination parameter – as did all ‘conservative’ cases. Only a handful of cases (fifteen) had a negative discrimination parameter, and they were all cases that lacked a clear direction. Whether our recovered dimension runs from left to right or right to left, this finding implies that one side of the court was permanently in the majority, whilst the other side was permanently condemned to fruitless dissent. Such an interpretation is difficult to sustain, given the rough parity between ‘liberal’ and ‘conservative’ outcomes shown in Table 1.

The coefficients predicting these discrimination parameters also performed poorly. Although four out of five coefficients had the right sign, the coefficient was significantly different from zero at the 95 per cent level in only one case (public law). In one issue area – criminal law – the coefficient had the wrong sign, though again it was not readily distinguishable from zero.Footnote ³⁶

Thirdly, the judges’ positions, whilst superficially related to their politics, are not related to their positions in judging, but rather to their propensity to dissent. From Figure 2 it might seem that there is a powerful partisan division between the judges, with justices such as Lords Bingham and Scarman to the left of the median justice (Lord Hutton), and justices like Lords Ackner and Roskill to the right. There is a large cluster of Conservative appointees at the right end of the scale, and we can be confident that the median Labour appointee lies to the left of the median Conservative appointee ($ P[{{\tilde{\theta }}_{Lab}}\, \lt \,{{\tilde{\theta }}_{Cons}}]\, = \,0.82 $).Footnote ³⁷

This interpretation is strengthened by considering the known politics of these judges. Suppose we describe a judge as ‘conservative’ if he has contested a seat for the Conservative party, held a government post under a Conservative administration or been described by reliable commentators as a ‘conservative’ judge. Of the fourteen judges who qualify as ‘conservative’ based on these criteria (Ackner, Brightman, Diplock, Hobhouse, Millett and Roskill as conservative judges,Footnote ³⁸ and Clyde, Dilhorne, Fraser, Guest, Hailsham, Reid, Simon and Wilberforce as former Conservative or Unionist office holders or candidatesFootnote ³⁹, nine lie to the right of the median justice, Rodger of Earlsferry. Of the five remaining judges, one (Wilberforce) was an unsuccessful Conservative candidate before starting on the bench, two (Dilhorne and Simon of Glaisdale) were legal officers in Conservative governments and two (Lords Hobhouse and Millet) were perhaps only described as conservative in contrast to expectations about the Blair government's likely judicial appointments.

Conversely, suppose we describe as ‘progressive’ all those judges who have contested a seat for the Labour party or the Liberal party prior to World War II, held government posts under a Labour administration or been described by reliable commentators as ‘progressive’ or ‘liberal’. Of the five judges who can be described as progressive (Donovan, Salmon, Elwyn-Jones, Scarman and Morris of Borth-y-Gest),Footnote ⁴⁰ all but one – Lord Donovan – lie to the left of the median justice.

However, this interpretation of the recovered dimension as a conservative-liberal dimension is not borne out by more basic statistics on case outcomes. For each issue area, we can calculate a judge's raw ‘liberalism score’ – the percentage of times s/he voted in a notionally liberal direction, as described in Table 1. Although the correlation between a judge's location and his/her raw liberalism score is negative, as expected, the correlation is very weak (r = −0.29) (see Figure 3a).

Fig. 3

Ideal points and judges’ voting. (a) Ideal points by liberalism; (b) Ideal points by dissent

Only one judge characteristic is reliably associated with their location. The correlation between judges’ rate of dissent and his/her location is highly significant (p < 0.001) and strong (r = −0.83) (see Figure 3b). This relationship suggests that the recovered dimension is not measuring differences between judges’ political attitudes, but rather their views about the usefulness of dissent, with justices to the left of the recovered dimension – Hale, Mustill, Morris and Hobhouse – more inclined to dissent than justices such as Hope of Craighead, Browne-Wilkinson or Roskill. This is the only explanation for why almost all of the discrimination parameters were positive – because judges who are favourably inclined to dissent are, tautologically, often in the minority.

If the recovered dimension does indicate judges’ propensity to dissent, how can we explain the moderate-to-strong relationship between their locations and the party that appointed them? Previous US research has shown that female judgesFootnote ⁴¹ and judges from non-traditional backgroundsFootnote ⁴² are more likely to author dissenting opinions. Labour nominated the only female Law Lord (Baroness Hale), as well as six of the eleven judges who were not educated at fee-paying schools, despite nominating far fewer judges (twenty-five to the Conservative party's thirty-nine). Whilst attending a state school may only be considered a ‘non-traditional’ background in the rarified atmosphere of the Lords, Labour appointees do differ in their background characteristics.

Conversely, the Conservative party nominated bare majorities of the Scottish (five to four) and Northern Irish (two to one) judges shown in Figure 2; they are clustered towards the right end of the recovered dimension. Of the nine judges who have practised at the Scottish bar or heard Scottish cases, only one – Jauncey of Tullichettle – is to the left of the median justice (Lord Rodger of Earlsferry, also Scottish). Indeed, we can be far more confident about differences between Scottish/non-Scottish judges than we can be about party differences: $ P[{{\tilde{\theta }}_{Scot}}\, \gt \,{{\tilde{\theta }}_{\neg Scot}}]\, = \,0.96 $.

This finding suggests that propensity to dissent is based on particular personal characteristics, rather than the idiosyncrasies of individual judges, and that appointees of different parties differ in those personal characteristics. Judges who specialize in English law (rather than Scots law or the law of Northern Ireland) and who come from non-traditional backgrounds, such as state schools or countries other than England (thus including both Welsh judges and judges such as Cooke, Pearson, Hoffmann and Steyn), are less likely to act deferentially towards English law in general and precedent in particular. Judges who specialize in Scots or Northern Irish law, whether from non-traditional backgrounds or not, act with greater deference in all cases, the majority of which involve English law. These personal characteristics may translate into differences in jurisprudence – ‘Scots judges have tended towards a… black-letter interpretative approach to the law’Footnote ⁴³ – but there is insufficient evidence of this. Only if we had a coding of the style of judicial opinions in terms of narrow, conservative holdings or broad, liberal holdings – in a fashion analogous to that given in Table 1 for case outcomes – could we demonstrate this.

Discussion

Thus far, I have shown that a particular model of decision making on the House of Lords Appellate Committee, where judges’ votes are expressions of their location along a single dimension, is a poorer model of voting than a simple null model, which predicts that each judge has the same probability of voting with the majority. Therefore, the judge locations plotted in Figure 2 should not be interpreted as positions in the political space.

This conclusion does not mean that judges’ decisions do not ‘reflect’ their attitudes in some other way. First, it is possible that a majority decision of a panel of judges is affected by the attitudes of the judges who comprise it, even if the individual decisions of panel members are not.Footnote ⁴⁴ This might be the case if judges seek consensus. Judges decide in part based on the draft opinions of their colleagues,Footnote ⁴⁵ and will ‘acquiesce or give a dubitante opinion’ in order to preserve unanimity.Footnote ⁴⁶ Judges are also less likely to reverse colleagues with whom they will have to work in the near future.Footnote ⁴⁷ Such behaviour violates the assumption of conditional independence that is found both in attitudinal models of judging and in the item response framework. Methods that treat the majority outcome as the explanandum, such as linear discriminant analysisFootnote ⁴⁸ or ecological item response theory,Footnote ⁴⁹ may therefore yield intelligible judge and case locations.

Secondly, the fact that the attitudinal model has been shown not to work in the Appellate Committee of the House of Lords does not necessarily mean that it will also fail for the new UK Supreme Court. Institutional features of the new court make it more conducive to dissent; more cases are heard by nine-judge panels, which were a rarity in the Lords; more cases result in a single majority opinion; and more cases deal with human rights claims.Footnote ⁵⁰ These innovations, respectively, increase the likelihood that a judge will disagree with the majority, and decrease the likelihood that a judge who disagrees will be able to finesse his or her disagreement by giving a doubtful concurrence. Consequently, whilst we ought not describe the ‘Law Lords’ as political, we may wish to reserve judgement on future members of the Supreme Court. We may find that the UK Supreme Court is at the same historical juncture as the US Supreme Court in the 1940s – on the brink of a collapse in the norm of consensus.Footnote ⁵¹

Footnotes

Lecturer in Politics, University of East Anglia (email: c.hanretty@uea.ac.uk). The author thanks John Greenaway, Baroness Hale, Simon Hix, Lindsay Stirton, Nick Vivyan, and the Journal's anonymous reviewers for extremely helpful comments on this article. Data replication sets are available at http://dx.doi.org/doi:10.1017/S0007123412000270.

¹ Hansard, 19 November 2001, col. 29.

² A & Others v. Secretary of State for the Home Department [2004 UKHL 56].

³ Martin, Andrew D. and Quinn, Kevin M., ‘Dynamic Ideal Point Estimation via Markov Chain Monte Carlo for the US Supreme Court, 1953–1999’, Political Analysis, 10 (2002), 134–53

⁴ Wood, Rebecca, ‘Dimensions of Decision Making: Determining the Complexity of Politics on the High Court of Australia’, paper presented at the Annual Meeting of the Southern Political Science Association, Savannah, Georgia, 2002

⁵ Alarie, Benjamin and Green, Andrew, ‘The Reasonable Justice: An Empirical Analysis of Justice Frank Iacobuccis Career on the Supreme Court of Canada’, University of Toronto Law Journal, 47 (2007), 195–226

⁶ Robertson, David, ‘Judicial Ideology in the House of Lords: A Jurimetric Analysis’, British Journal of Political Science, 12 (1982), 1–25

Robertson, David, Judicial Discretion in the House of Lords (Oxford: Oxford University Press, 1998)

⁷ Hodder-Williams, Richard, ‘Six Notions of Political and the United States Supreme Court’, British Journal of Political Science, 22 (1992), 1–20

⁸ Volcansek, Mary L., ‘Constitutional Courts as Veto Players: Divorce and Decrees in Italy’, European Journal of Political Research, 39 (2001), 347–72

⁹ Drewry, Gavin, ‘Judges and Political Inquiries: Harnessing a Myth’, Political Studies, 23 (1975), 49–61

¹⁰ Segal, Jeffrey A. and Spaeth, Harold J., The Supreme Court and the Attitudinal Model (Cambridge: Cambridge University Press, 1993)

¹¹ Clayton, Cornell W. and Gillman, Howard, Supreme Court Decision-Making: New Institutionalist Approaches (Chicago: University of Chicago Press, 1999)

Thomas H. Hammond, Chris W. Bonneau and Reginald S. Sheehan, Strategic Behavior and Policy Choice on the US Supreme Court (Stanford University Press, 2005)

Sunstein, Cass R., Schkade, DavidEllman, Lisa and Sawicki, Andres, Are Judges Political?: An Empirical Analysis of the Federal Judiciary (Washington, DC: Brookings Institution Press, 2006)

¹² This second strategy is employed by Robertson, Judicial Discretion in the House of Lords.

¹³ Tomasic, Roman ed., Understanding Lawyers: Perspectives on the Legal Profession in Australia (Sydney: Law Foundation of New South Wales, 1978)

¹⁴ Robertson, ‘Judicial Ideology in the House of Lords’, p. 10

¹⁵ J.A.G. Griffith, The Politics of the Judiciary, 3rd edn. (London: Fontana, 1985), p. 199

¹⁶ Robertson, Judicial Discretion in the House of Lords, p. 401

¹⁷ Lee, Simon, Judging Judges (London: Faber and Faber, 1988)

¹⁸ Robertson, ‘Judicial Ideology in the House of Lords’

¹⁹ Dubois, Philip L. and Dubois, Paul F., ‘Measuring Dissent Behavior on State Courts: An Application and an Adaptation of Known Measurement Techniques’, Polity, 13 (1980), 147–58

²⁰ Haynie, Stacie L., Sheehan, Reginald S.Songer, Donald R. and Tate, C. Neal, ‘High Courts Judicial Database: Version 1.1’, 2007, downloaded December 2009

²¹ In the model of judicial decision making that I use, unanimous decisions provide no information about the relative or absolute positions of the judges. While it is true that panels of judges may unanimously give decisions that seem to be particularly left wing or right wing, it does not necessarily follow that the judges who decided those cases were particularly left wing or right wing. Non-unanimous cases, by contrast, allow us to identify differences between justices that may reflect attitudes towards public policy.

²² Disagreements over rationes may be informative about judges’ politics, but are not relevant to the analysis I present here.

²³ Lords Emslie, Irvine of Lairg, Taylor of Gosforth, Havers, Wheatley, Avonside and Parker of Waddington.

²⁴ This (North American-influenced) coding of cases may seem strange to British lawyers, who might expect left-leaning judges to find against the state in public law, particularly in immigration and deportation disputes.

²⁵ Jackman, Simon, ‘Bayesian Analysis for Political Research’, Annual Review of Political Science, 7 (2004), 483–505

²⁶ Clinton, JoshuaJackman, Simon and Rivers, Douglas, ‘The Statistical Analysis of Roll Call Data’, American Political Science Review, 98 (2004), 355–70

²⁷ Online supplementary information shows that my findings are not sensitive to the choice of approach to modelling the discrimination parameter.

²⁸ Rasch, Georg, Probabilistic Models for Some Intelligence and Attainment Tests (Copenhagen: Danish Institute for Educational Research, 1960)

²⁹ Bafumi, Joseph, Gelman, AndrewPark, David K. and Kaplan, Noah, ‘Practical Issues in Implementing and Understanding Bayesian Ideal Point Estimation’, Political Analysis, 13 (2005), p. 171

³⁰ Jackman, Simon, ‘Multidimensional Analysis of Roll Call Data via Bayesian Simulation: Identification, Estimation, Inference, and Model Checking’, Political Analysis, 9 (2001), p. 227

³¹ This model in no way constrains cases of a certain directionality to discriminate with respect to the recovered dimension: the credible intervals surrounding the coefficients γ ₁_k are extremely large and encompass zero.

³² Bridge and Griffiths were chosen because they lay at opposite ends of Robertson's 1998 ‘constitutionalism’ dimension, with Bridge more likely to find in favour of appellants alleging infringement of their civil rights.

³³ Values of Geweke's diagnostic were within the range ±1.96 for all but two judges. Trace plots are available on request.

³⁴ The percentage reduction in error (PRE) for each vote is the number of votes in the minority, minus the number of incorrect predictions, divided by the number of votes in the minority. A perfectly predicted vote has an PRE of 1. The APRE is simply the PRE averaged over all votes.

³⁵ The GMP is the exponential of the average log-likelihood.

³⁶ These coefficients are not reported here, but are available on request.

³⁷ Note that, though Viscount Dilhorne was appointed a Lord of Appeal in Ordinary by the Wilson government, he is considered a Conservative appointee, as he previously served as Lord Chancellor under Macmillan and Douglas-Home.

³⁸ Ackner: ‘unashamedly conservative’ (Michael Beloff, ‘Ackner, Desmond James Conrad, Baron Ackner (1920–2006), Oxford Dictionary of National Biography, 2010)

Brightman: ‘[s]een as conservative and relatively pro-Executive’ (obituary, Daily Telegraph, 8 February 2006)

Sedley, Stephen and Quesne, Godfray Le, ‘Diplock (William John) Kenneth, Baron Diplock (1907–1985)’, Oxford Dictionary of National Biography, 2010

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⁴² Hettinger, Virginia A.Lindquist, Stefanie A. and Martinek, Wendy L., ‘Comparing Attitudinal and Strategic Accounts of Dissenting Behavior on the US Courts of Appeals’, American Journal of Political Science, 48 (2004), 123–37

⁴³ ONeill, Aidan, ‘Judging Democracy: The Devolutionary Settlement and the Scottish Constitution’, Edinburgh Law Review, 8 (2004), p. 186

⁴⁴ Sunstein et al., Are Judges Political? (in particular, Table 2.1 and pp. 38–39).

⁴⁵ Jacob, Robin, ‘Intellectual Property’, in Blom-Cooper, Dickson and Drewry, The Judicial House of Lords 1876–2009, pp. 716–17

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⁴⁷ Vidal, Jordi Blanes i and Leaver, Clare, ‘Using Group Transitions to Estimate the Effect of Social Interactions on Judicial Decisions’, unpublished working paper, 2010

⁴⁸ Robertson, Judicial Discretion in the House of Lords.

⁴⁹ Malecki, Michael, ‘Judicial Behavior Behind Mask and Shield: Modeling the European Court of Justice’, paper presented at the Annual Meeting of the American Political Science Association, 2009

⁵⁰ Arvind, T.T. and Stirton, Lindsay, ‘Judicial Decision-Making in the House of Lords: A Preliminary Analysis’, paper presented at the Annual Meeting of the Political Studies Association, London, 2011

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* Lecturer in Politics, University of East Anglia (email: c.hanretty@uea.ac.uk). The author thanks John Greenaway, Baroness Hale, Simon Hix, Lindsay Stirton, Nick Vivyan, and the Journal's anonymous reviewers for extremely helpful comments on this article. Data replication sets are available at http://dx.doi.org/doi:10.1017/S0007123412000270.