Barbey & Sloman (B&S) provide a convincing account of the contributions of associative and rule-based cognitive processes to base-rate respect. Absent from their model, however, is a consideration of the effects of psychological motivations on the use of statistical rules. The sorts of motivations known to influence the use of statistical rules fall into three general categories: ego-justifying, group-justifying, and system-justifying (Jost & Banaji Reference Jost and Banaji1994).
Ego-justifying neglect of base rates occurs in evaluations of medical diagnoses. For example, Ditto et al. (Reference Ditto, Scepansky, Munro, Apanovitch and Lockhart1998) told participants that they had tested positive for an enzyme (TAA) whose presence was predictive of immunity or vulnerability to pancreatic disease. Individuals in the “healthy consequences” condition were told that TAA made it less likely they would get pancreatic disease, whereas individuals in the “unhealthy consequences” condition were informed that TAA increased their chance of getting pancreatic disease. Participants were also told either that the test was highly accurate (1 in 200 failure rate), or relatively inaccurate (1 in 10 failure rate). Participants who were told that their TAA levels put them at risk for pancreatic disease and that the test was relatively inaccurate, perceived the diagnosis as less accurate than participants in the high accuracy condition – a normatively defensible application of the base rate. But participants who were told that their TAA levels reduced the risk of pancreatic disease, and were further informed that the test was inaccurate, were just as likely as participants in the high accuracy conditions to perceive the diagnosis as accurate.
Base-rate neglect can also be driven by bias in favor of one's social group (Ginossar & Trope Reference Ginossar and Trope1987; Schaller Reference Schaller1992). In one study, the male employees of an organization were described as stronger leaders than the female employees (Schaller Reference Schaller1992). However, there was an additional, much more predictive base rate at work: participants were also told that male employees were dramatically more likely than female employees to be assigned to serve in an executive role. In other words, the males were stronger leaders because more of them were assigned to serve in leadership roles. Making the normatively rational judgment, female participants took into account the base rate of males and females in executive roles and concluded that male and female employees were equally talented leaders. But male participants neglected the assignment of male and female employees into different organizational roles, concluding that male employees were superior leaders. A separate experiment revealed that female participants were likewise biased in favor of their own group. These female participants ignored the base rate of male and female executives when it led them to the (incorrect) conclusion that female employees were superior leaders. In sum, participants neglected a base rate when it allowed them to draw a conclusion favorable to their own gender.
The motivation to uphold the social hierarchy (i.e., system justification) also plays a role in the application of base rates about racial groups to individual group members (McDell et al. Reference McDell, Uhlmann, Omoregie and Banaji2006; Tetlock et al. Reference Tetlock, Kristel, Elson, Green and Lerner2000). Individuals who are non-prejudiced toward Black Americans make similar estimates of group crime rates among White and Black Americans as prejudiced individuals do. However, only the prejudiced individuals (i.e., those who have a motivation to uphold the social hierarchy) endorse the use of base rates to discriminate against an individual Black person. Individuals who endorse social hierarchies based on groups competing for power (a so-called “social dominance orientation”; Sidanius & Pratto Reference Sidanius and Pratto1999), are also more likely to endorse the application of base rates to individuals.
These biasing psychological motives likely work through the recruitment of the cognitive processes described by B&S. For example, research has demonstrated that social-psychological motives moderate whether associative or rule-based cognitive processes are employed in the first place. Ditto et al. (Reference Ditto, Scepansky, Munro, Apanovitch and Lockhart1998) presented evidence that people expend little cognitive effort when presented with information that favors a desired conclusion – they quickly accept it with minimal deliberation. Conversely, when presented with undesired information (that is, information inconsistent with one of the aforementioned motives), individuals seem especially likely to recruit rule-based, deliberative thinking in an effort to discredit the undesired information.
Ego-justification, group-justification, and system-justification motives are difficult to defend as rational influences on the use of statistical rules in social judgments. Although a person motivated by racial prejudice may make a “correct” judgment (i.e., a close approximation to the answer Bayes' Theorem would formally provide) when assessing the probability that a member of another race is a criminal, few would argue that this is due to statistical reasoning. Here we can distinguish between the rationality of the belief and the rationality of the process that led to that belief. Because social motivations easily (and often) lead to error, they make for suspicious guides to truth. Relying on them to achieve a rational belief is like throwing darts to choose stock winners. One may pick the best stocks, but surely it was by accident. Indeed, many people would reject the influence of these biases if they were made aware of them (i.e., such motives fail the test of subjective rationality; Pizarro & Uhlmann Reference Pizarro and Uhlmann2005).
An emphasis on social-psychological motivations may lead not only to a more complete understanding of base-rate neglect, but may also enrich a variety of cognitive theoretical approaches to human judgment. The human mind may possess specific mechanisms (e.g., in-group loyalty) that were adaptive because they aided in the individual's survival in an inherently social environment. Therefore, it may be important to consider such influences when accounting for phenomena that, at first, appear to be non-social in nature. For example, basic cognitive processes such as induction from property clusters contribute to biological explanations for natural kinds (Gelman Reference Gelman2003, Keil Reference Keil1989). Yet, recent studies demonstrate that system-justifying motives may lead people to endorse biological explanations such that explaining group differences as “natural” helps justify their continued existence (Brescoll & Uhlmann Reference Brescoll and Uhlmann2007). Thus, applying social-psychological motives to theories of cognitive processes may lead to a more complex, but hopefully also more accurate, portrait of human cognition.
