In this commentary, I do not directly argue against the findings of Barbey & Sloman (B&S). However, I note that the range of base rate discounting effects under nearly (apparently) identical circumstances is roughly as large as the effect itself. This strongly suggests that important factors are not being addressed. I provide three suggestions for what some of these factors might be.
First, in the real world, people do not typically experience true randomness. In the natural as well as the artificial world, things are typically arranged in a “clumped” fashion. Given that the natural world in which we have evolved as well as the world that we have constructed are both non-random, it would be a priori rather amazing if we humans somehow developed a natural penchant for dealing with frequencies of randomly occurring events. The conservatism shown in probability estimations is consistent with a bias toward believing in the “clumpiness” of distributions.
Not only do artifacts drawn from the natural and artificial worlds tend to “start out” in non-random clumps, but many mechanical and social processes are such that even if an explicit attempt is made to produce randomness, any interruption or incompleteness in that process is likely to result in something that is less than truly random. To give a simple example, if one takes a small canister of black balls, pours them into a larger bin, adds a small canister of white balls on top, and then begins shaking them together, at every point until randomness is achieved, there are likely to be a disproportionate number of white balls on top. Note that this process is very asymmetrical. Therefore, if an experimenter who purports to present a subject with a “random mixture” makes any reasonable kind of error (does not shake long enough, shakes in such a way that layers are not intermixed), the result is that some degree of “clumpiness” will persist.
Second, in the social world, communication is not a mere encoding of what is. More often, there is communicative purpose to communications. Better than an “encoding-decoding” model is a “design-interpretation” model of human-to-human communication (Thomas Reference Thomas1978). How people relate to propositions presented to them is complexly influenced by the inferred motives of those who present the information. It would be astounding if every subject in a psychological experiment simply and naively believed everything an experimenter presented about the purpose and context of the experiment. Even if a subject presumes that they are engaged in a “purely cooperative” effort with the experimenter, conversational postulates will still hold (Grice Reference Grice and Cole1978). These imply that the experimenter only presents data that are necessary and sufficient for the task. Further, what a particular subject views as “real news” depends on what they already know (Clark & Brennan Reference Clark, Brennan, Resnick, Levine and Teasley1991). If an experimenter says that “the earth has one natural satellite,” because subjects already know this, they will tend to assume that this is a set-up for a conversation about artificial satellites. When statements are presented about cancer rates, tests, and so on, subjects may evaluate these statements in light of what they already know about these topics. In addition, subjects make some sort of assessment of why they are being told. The “real” motive, from the perspective of the experimenter – namely, to determine general characteristics of human cognition – may be a common motive among the experimenter's peers, but it is not a motive widely shared in the larger society. Indeed, to many subjects, this may seem to be a cover story for an assessment of their personal capabilities. The assumptions of rhetorical purpose may well interact with the obviousness of the representation. Mood and personality will tend to play a bigger part in the interpretation of an inkblot than in the interpretation of a relatively clear and unambiguous stimulus.
Many of the specific findings reviewed in the target article are understandable from this perspective. For instance, more concrete and specific statements are more believable and more likely to be taken at face value because they are more subject to verification or disproval. University prestige may well make a difference in terms of source credibility, rather than the general intelligence of the subjects. If subjects are paid, there is more chance in our society of legal repercussions for lying or deception, and awareness of this factor also increases source credibility.
Third, a particularly common rhetorical context is storytelling. People deal with stories both in personal interaction and in explicit entertainment contexts such as television, movies, and novels. Stories in these latter contexts are not typically told to communicate about representative situations, but rather, concern the “edges” of human experience, the exceptions, the rare and unusual (McKee Reference McKee1997). Therefore, it is natural that when one is told a story, one tends to assume purposeful dramatic action. In a movie, if someone goes to the doctor for a diagnostic test for some rare disease, the person is much more likely to have that disease than would be predicted by statistics. Furthermore, writers choose details for rhetorical purpose. For instance, if someone in a soap opera walks into a room and they look like a professional football player, the chances are actually high that they are a professional football player and not an accountant or salesperson.
These three potentially confounding influences do not mean that better predictability is impossible in this paradigm. There may be an analogy with measuring sensory thresholds. Trying to measure absolute thresholds by asking people whether or not they hear a sound can be very sensitive to expectations, set, and motivation. Asking subjects to specify in which of two intervals a sound appeared is much less sensitive to these social variables. A forced choice paradigm should also work in this context to minimize the potentially confounding effects recounted above.
