Individual Differences in Reasoning: Implications for the Rationality Debate?

BEHAVIORAL AND BRAIN SCIENCES (2000) 23, 645–726 Printed in the United States of America Individual differences in reasoning: Implications for the rationality debate? Keith E. Stanovich Department of Human Development and Applied Psychology, University of Toronto, Toronto, Ontario, Canada M5S 1V6 [email protected] Richard F.West School of Psychology, James Madison University, Harrisonburg, VA 22807 [email protected] falcon.jmu.edu//~westrf Abstract: Much research in the last two decades has demon- and they display numerous other information processing bi- strated that human responses deviate from the performance ases (for summaries of the large literature, see Baron 1994; deemed normative according to various models of decision mak- 1998; Evans 1989; Evans & Over 1996; Kahneman et al. ing and rational judgment (e.g., the basic axioms of utility theory). 1982; Newstead & Evans 1995; Nickerson 1998; Osherson This gap between the normative and the descriptive can be inter- 1995; Piattelli-Palmarini 1994; Plous 1993; Reyna et al., in preted as indicating systematic irrationalities in human cognition. press; Shafir 1994; Shafir & Tversky 1995). Indeed, demon- However, four alternative interpretations preserve the assumption that human behavior and cognition is largely rational. These posit strating that descriptive accounts of human behavior di- that the gap is due to (1) performance errors, (2) computational verged from normative models was a main theme of the so- limitations, (3) the wrong norm being applied by the experi- called heuristics and biases literature of the 1970s and early menter, and (4) a different construal of the task by the subject. In 1980s (see Arkes & Hammond 1986; Kahneman et al. the debates about the viability of these alternative explanations, 1982). attention has been focused too narrowly on the modal response. The interpretation of the gap between descriptive mod- In a series of experiments involving most of the classic tasks in the els and normative models in the human reasoning and de- heuristics and biases literature, we have examined the implica- cision making literature has been the subject of con- tions of individual differences in performance for each of the four tentious debate for almost two decades (a substantial explanations of the normative/descriptive gap. Performance er- portion of that debate appearing in this journal; for sum- rors are a minor factor in the gap; computational limitations un- derlie non-normative responding on several tasks, particularly maries, see Baron 1994; Cohen 1981; 1983; Evans & Over those that involve some type of cognitive decontextualization. Un- 1996; Gigerenzer 1996a; Kahneman 1981; Kahneman & expected patterns of covariance can suggest when the wrong norm Tversky 1983; 1996; Koehler 1996; Stein 1996). The de- is being applied to a task or when an alternative construal of the task should be considered appropriate. Keywords: biases; descriptive models; heuristics; individual dif- Keith E. Stanovich is Professor of Human Develop- ferences; normative models; rationality; reasoning ment and Applied Psychology at the University of Toronto. He is the author of more than 125 scientific ar- ticles in the areas of literacy and reasoning, including Who Is Rational? Studies of Individual Differences in 1. Introduction Reasoning (Erlbaum, 1999). He is a Fellow of the APA and APS and has received the Sylvia Scribner Award A substantial research literature – one comprising literally from the American Educational Research Association hundreds of empirical studies conducted over nearly three for contributions to research. Richard F. West is a Professor in the School of Psy- decades – has firmly established that people’s responses of- chology at James Madison University, where he has ten deviate from the performance considered normative on been named a Madison Scholar. He received his Ph.D. many reasoning tasks. For example, people assess proba- in Psychology from the University of Michigan. The au- bilities incorrectly, they display confirmation bias, they test thor of more than 50 publications, his main scientific in- hypotheses inefficiently, they violate the axioms of utility terests are the study of rational thought, reasoning, de- theory, they do not properly calibrate degrees of belief, they cision making, the cognitive consequences of literacy, overproject their own opinions on others, they allow prior and cognitive processes of reading. knowledge to become implicated in deductive reasoning, © 2000 Cambridge University Press 0140-525X/00 $12.50 645 Stanovich & West: Individual differences in reasoning bate has arisen because some investigators wished to in- 2. Performance errors terpret the gap between the descriptive and the normative as indicating that human cognition was characterized by Panglossian theorists who argue that discrepancies be- systematic irrationalities. Owing to the emphasis that these tween actual responses and those dictated by normative theorists place on reforming human cognition, they were models are not indicative of human irrationality (e.g., Co- labeled the Meliorists by Stanovich (1999). Disputing this hen 1981) sometimes attribute the discrepancies to perfor- contention were numerous investigators (termed the Pan- mance errors. Borrowing the idea of a competence/perfor- glossians; see Stanovich 1999) who argued that there were mance distinction from linguists (see Stein 1996, pp. 8–9), other reasons why reasoning might not accord with nor- these theorists view performance errors as the failure to ap- mative theory (see Cohen 1981 and Stein 1996 for exten- ply a rule, strategy, or algorithm that is part of a person’s sive discussions of the various possibilities) – reasons that competence because of a momentary and fairly random prevent the ascription of irrationality to subjects. First, in- lapse in ancillary processes necessary to execute the strat- stances of reasoning might depart from normative stan- egy (lack of attention, temporary memory deactivation, dis- dards due to performance errors – temporary lapses of traction, etc.). Stein (1996) explains the idea of a perfor- attention, memory deactivation, and other sporadic infor- mance error by referring to a “mere mistake” – a more mation processing mishaps. Second, there may be stable colloquial notion that involves “a momentary lapse, a diver- and inherent computational limitations that prevent the gence from some typical behavior. This is in contrast to at- normative response (Cherniak 1986; Goldman 1978; Har- tributing a divergence from norm to reasoning in accor- man 1995; Oaksford & Chater 1993; 1995; 1998; Stich dance with principles that diverge from the normative 1990). Third, in interpreting performance, we might be ap- principles of reasoning. Behavior due to irrationality con- plying the wrong normative model to the task (Koehler notes a systematic divergence from the norm” (p. 8). Simi- 1996). Alternatively, we may be applying the correct nor- larly, in the heuristics and biases literature, the term bias is mative model to the problem as set, but the subject might reserved for systematic deviations from normative reason- have construed the problem differently and be providing ing and does not refer to transitory processing errors (“a the normatively appropriate answer to a different problem bias is a source of error which is systematic rather than ran- (Adler 1984; 1991; Berkeley & Humphreys 1982; Broome dom,” Evans 1984, p. 462). 1990; Hilton 1995; Schwarz 1996). Another way to think of the performance error explana- However, in referring to the various alternative explanation is to conceive of it within the true score/measurement tions (other than systematic irrationality) for the normative/ error framework of classical test theory. Mean or modal descriptive gap, Rips (1994) warns that “a determined skep- performance might be viewed as centered on the norma- tic can usually explain away any instance of what seems at tive response – the response all people are trying to ap- first to be a logical mistake” (p. 393). In an earlier criticism proximate. However, scores will vary around this central of Henle’s (1978) Panglossian position, Johnson-Laird tendency due to random performance factors (error vari- (1983) made the same point: “There are no criteria inde- ance). pendent of controversy by which to make a fair assessment It should be noted that Cohen (1981) and Stein (1996) of whether an error violates logic. It is not clear what would sometimes encompass computational limitations within count as crucial evidence, since it is always possible to pro- their notion of a performance error. In the present target vide an alternative explanation for an error” (p. 26). The article, the two are distinguished even though both are most humorous version of this argument was made by Kah- identified with the algorithmic level of analysis (see Ander- neman (1981) in his dig at the Panglossians who seem to son 1990; Marr 1982; and the discussion below on levels of have only two categories of errors, “pardonable errors by analysis in cognitive theory) because they have different im- subjects and unpardonable ones by psychologists” (p. 340). plications for covariance relationships across tasks. Here, Referring to the four classes of alternative explanations dis- performance errors represent algorithmic-level problems cussed above – performance errors, computational limita- that are transitory in nature. Nontransitory problems at the tions, alternative problem construal, and

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