The similarity heuristic

Decision makers often make snap judgments using fast‐and‐frugal decision rules called cognitive heuristics. Research into cognitive heuristics has been divided into two camps. One camp has emphasized the limitations and biases produced by the heuristics; another has focused on the accuracy of heuristics and their ecological validity. In this paper we investigate a heuristic proposed by the first camp, using the methods of the second. We investigate a subset of the representativeness heuristic we call the “similarity” heuristic, whereby decision makers who use it judge the likelihood that an instance is a member of one category rather than another by the degree to which it is similar to others in that category. We provide a mathematical model of the heuristic and test it experimentally in a trinomial environment. In this environment, the similarity heuristic turns out to be a reliable and accurate choice rule and both choice and response time data suggest it is also how choices are made. We conclude with a theoretical discussion of how our work fits in the broader “fast‐and‐frugal” heuristics program, and of the boundary conditions for the similarity heuristic. Copyright © 2009 John Wiley & Sons, Ltd.     

Covariation assessment in rank order data

Two experiments were conducted to investigate how individuals assess covariation with rank order data. In both studies, subjects were given sets of rank order data, each set consisting of ten items ranked on two characteristics, and were asked to estimate the degree of relationship for each set. Contrary to previous research, subjects' estimates of covariation in this task were quite sensitive to actual levels of correlation in the data and remained unaffected by simple variations in the way rank order data were presented. More importantly, it appeared that this sensitivity to covariation was due likely to the use of a simple heuristic referred to here as the total discrepancy heuristic. These findings are discussed in terms of the availability of simple heuristics in rank-ordered versus other types of data and the consequences of using such heuristics in decision-making contexts.     

Not so fast! (and not so frugal!): rethinking the recognition heuristic

The 'fast and frugal' approach to reasoning (Gigerenzer, G., & Todd, P. M. (1999). Simple heuristics that make us smart. New York: Oxford University Press) claims that individuals use non-compensatory strategies in judgment--the idea that only one cue is taken into account in reasoning. The simplest and most important of these heuristics postulates that judgment sometimes relies solely on recognition. However, the studies that have investigated usage of the recognition heuristic have confounded recognition with other cues that could also lead to similar judgments. This paper tests whether mere recognition is actually driving the findings in support of the recognition heuristic. Two studies provide evidence that judgments do not conform to the recognition heuristic when these confounds are accounted for. Implications for the study of simple heuristics are discussed.     

We favor formal models of heuristics rather than lists of loose dichotomies: a reply to Evans and Over

In their comment on Marewski et al. (good judgments do not require complex cognition, 2009) Evans and Over (heuristic thinking and human intelligence: a commentary on Marewski, Gaissmaier and Gigerenzer, 2009) conjectured that heuristics can often lead to biases and are not error free. This is a most surprising critique. The computational models of heuristics we have tested allow for quantitative predictions of how many errors a given heuristic will make, and we and others have measured the amount of error by analysis, computer simulation, and experiment. This is clear progress over simply giving heuristics labels, such as availability, that do not allow for quantitative comparisons of errors. Evans and Over argue that the reason people rely on heuristics is the accuracy-effort trade-off. However, the comparison between heuristics and more effortful strategies, such as multiple regression, has shown that there are many situations in which a heuristic is more accurate with less effort. Finally, we do not see how the fast and frugal heuristics program could benefit from a dual-process framework unless the dual-process framework is made more precise. Instead, the dual-process framework could benefit if its two “black boxes” (Type 1 and Type 2 processes) were substituted by computational models of both heuristics and other processes.     

On-line versus memory-based orientations and self-report validity

A partial replication of a study by Nisbett and Bellows (1977) to which a memorization condition was added showed that subjects did not have introspective access to the determinants of their judgments, but did so only in the impression-formation condition. In the memorization condition, the subjects' self-reports matched the observed experimental effects. An analysis of the results showed that this was probably because the subjects' judgments in the latter condition were based on causal theories. ©1997 John Wiley & Sons, Ltd.     

Judging risk behaviour and risk preference: The role of the evaluative connotation of risk terms

Two experiments investigate the impact of the evaluative connotation of risk terms on the judgment of risk behaviour and on risk preference. In the first experiment we focus on (1) the evaluation congruence of the risk terms with a general risk norm and (2) with subjects' individual risk preference, and its effects on the extremity of judgments of risk behaviour. In the second experiment we address (3) the effects of evaluative connotation of risk terms on risk preference. In the first experiment subjects were presented with four decision problems, each with a risky and a cautious decision option, and were required to judge options. Results showed that the judged discrepancy between the risky and cautious option was larger on scales which were evaluatively congruent with the general risk norm for that specific decision problem or with subjects' individual preference. More specificly, in decision problems for which there was considerable consensus about the risk-norm judgments were more extreme on scales which were congruent with the risk norm, in those problems lacking a clear-cut risk-norm judgments were more extreme on scales congruent with subjects' individual risk preference. In the second experiment we studied the reverse relation between the evaluative connotation of risk terms and risk preference. This experiment demonstrates that using evaluatively biased risk terms can affect risk preference. Using terms which imply a positive evaluation of risk-taking and a negative evaluation of risk avoidance led to increased risk preference, and vice versa. Results are discussed in the context of accentuation theory.     

Depressive realism and clinical depression

Depressive realism suggests that depressed individuals make more accurate judgments of control than their nondepressed counterparts. However, most studies demonstrating this phenomenon were conducted in nonclinical samples. In this study, psychiatric patients who met criteria for major depressive disorder underestimated control in a contingent situation and were consistently more negative in their judgments than were nondepressed controls. Depressed patients were less likely than their nondepressed counterparts to overestimate control in a noncontingent situation, but largely because they perceived receiving less reinforcement. Depressed patients were no more likely to use the appropriate logical heuristic to generate their judgments of control than their nondepressed counterparts and each appeared to rely on different primitive heuristics. Depressed patients were consistently more negative than their nondepressed counterparts and when they did appear to be more “accurate” in their judgments of control (as in the noncontingent situation) it was largely because they applied the wrong heuristic to less accurate information. These findings do not support the notion of depressive realism and suggest that depressed patients distort their judgments in a characteristically negative fashion.     

The “Black Sheep Effect”: Extremity of judgments towards ingroup members as a function of group identification

The present study proposes an extension to the phenomenon of ingroup favouritism, based on the hypothesis that judgments about ingroup members may be more positive or more negative than judgments about similar outgroup members. It contrasts predictions issued from the complexity-extremity hypothesis (Linville, 1982; Linville and Jones, 1980), from the ingroup favouritism hypothesis (Tajfel, 1982) and from Tesser's (1978; Millar and Tesser, 1986) attitude polarization model. Our main prediction, based on Social Identity Theory, is that judgments about both likeable and unlikeable ingroup members are more extreme than judgments about outgroup members. This phenomenon, coined the Black Sheep Effect, is viewed as due to the relevance that ingroup members'behaviour, as compared to that of outgroup members, has for the subjects' social identity. Three experiments supported our predictions. Experiment I additionally showed that inter-trait correlations were stronger for the ingroup than for the outgroup. Experiment 2 showed that the black sheep effect occurs only when the judgmental cues are relevant for the subjects' social identity, and Experiment 3 showed that levels of information about the target of the judgment were ineffective in generating judgmental extremity. Results are discussed in light of a cognitive-motivational alternative explanation to a purely cognitive interpretation of outgroup homogeneity.     

Representativeness and fallacies of probability judgment

Representativeness is the name given to the heuristic people often employ when they judge the probability of a sample by how well it represents certain salient features of the population from which it was drawn. The representativeness heuristic has also been used to account for how people judge the probability that a given population is the source of some sample. The latter probability, however, depends on other factors (e.g., the population's prior probability) as well as on the sample characteristics. A review of existing evidence suggests that the ignoring of such factors, a central finding of the heuristics approach to judgment under uncertainty, is a phenomenon which is conceptually distinct from the representativeness heuristic. These factors (base rates, sample size, and predictability) do not always exert the proper influence on people's first-order probability judgments, but they are not ignored when people make second-order (i.e., confidence) judgments. Other fallacies and biases in subjective evaluations of probability are, however, direct causal results of the employment of representativeness. For example, representativeness may be applied to the wrong features. Most devastating, perhaps, is that subjective probability judgments obey a logic of representativeness judgments, even though probability ought to obey an altogether different logic. Yet although the role of representativeness judgments in probability estimation leaves a lot to be desired, it is hard to envision prediction and inference completely unaided by representativeness.     

Understanding collision dynamics

In two experiments we investigated people's ability to judge the relative mass of two objects involved in a collision. It was found that judgments of relative mass were made on the basis of two heuristics. Roughly stated, these heuristics were (a) an object that ricochets backward upon impact is less massive than the object that it hit, and (b) faster moving objects are less massive. A heuristic model of judgment is proposed that postulates that different sources of information in any event may have different levels of salience for observers and that heuristic access is controlled by the rank ordering of salience. It was found that observers ranked dissimilarity in mass on the basis of the relative salience of angle and velocity information and not proportionally to the distal mass ratio. This heuristic model was contrasted with the notion that people can veridically extract dynamic properties of motion events when the kinematic data are sufficient for their specification.     

Information search in heuristic decision making

Simple heuristics of the type introduced by Gigerenzer, Todd, and The ABC Research Group ( 1999 ) embody principles for information search, stop and decision making. These heuristics suggest that such processes are simple. In an analysis of general practitioners' (GPs) information search and decision‐making behaviour when prescribing a lipid lowering drug, we examined whether information search was simple, and whether a heuristic that predicts a simple decision‐making process was also accurate at describing information search. We found that GPs' information search behaviour was simple in that it demonstrated characteristics of the matching heuristic (e.g. stopping rule). In addition, although the matching heuristic which correctly predicted on average 75% of GPs' decisions used significantly fewer cues on average than the GPs did in the information search task, it was reasonably accurate in describing order of information search. These findings have implications for the validity of simple heuristics describing both information search and decision making. Copyright © 2009 John Wiley & Sons, Ltd.     

Suppressing natural heuristics by formal instruction: The case of the conjunction fallacy

A basic principle of probability is the conjunction rule, p(B) p(A&B). People violate this rule often, particularly when judgments of probability are based on intensional heuristics such as representativeness and availability. Though other probabilistic rules are obeyed with increasing frequency as people's levels of mathematical talent and training increase, the conjunction rule generally does not show such a correlation. We argue that this recalcitrance is not due to inescapable “natural assessments”; rather, it stems from the absence of generally useful problem-solving designs that bring extensional principles to bear on this class of problem. We predict that when helpful extensional strategies are made available, they should compete well with intensional heuristics. Two experiments were conducted, using as subjects adult women with little mathematical background. In Experiment 1, brief training on concepts of algebra of sets, with examples of their use in solving problems, reduced conjunction-rule violations substantially, compared with a control group. Evidence from similarity judgments suggested that use of the representativeness heuristic was reduced by the training. Experiment 2 confirmed these training effects and also tested the hypothesis that conjunction-rule violations are due to misunderstanding of “B” as “B and not A.” Changes in detailed wording of the propositions to be ranked produced substantial effects on judgment, but the pattern of these effects supported the hypothesis that, for the type of problem used here, most conjunction errors are due to use of representativeness or availability. We conclude that such intensional heuristics can be suppressed when alternative strategies are taught.     

Rarely Occurring Headaches and Rarely Occurring Blindness: Is Rarely=Rarely? The Meaning of Verbal Frequentistic Labels in Specific Medical Contexts

In three experimental studies, factors were examined which might influence the interpretation of verbal frequentistic labels in a specific context (i.e. side effects of medical drugs). In Study 1, we directly assessed subjects' numerical equivalents of three verbal labels (recommended for use by the German Federal Health Agency), which were embedded in stylized leaflets for medical drugs; we compared the estimates with those obtained in a context-free situation. The major findings were that (1) subjects' numerical equivalents for the verbal labels were clearly lower in the context condition than in the context-free situation, (2) subjects'; interpretations appeared to depend on the seriousness of the side effects, but (3) this dependency disappeared when explicit base rates were provided. In Studies 2 and 3, we indirectly examined the influence of the seriousness of the side effects, their frequency, and of the mode of expression (verbally versus numerically) by asking for risk judgments for and choices between drugs. Results of particular importance were that (1) seriousness and frequency of side effects had the same influence on judgments and choices but the mode of expression had no significant effect on either judgments or choices; (2) when subjects’ individual numerical equivalents of verbal labels were used in the leaflets, numerically described drugs were judged equally risky as verbally described drugs but were significantly preferred for consumption. These findings have theoretical relevance for research on the processing of verbal and numerical frequentistic expressions as well as a number of practical implications for the communication of medical information.     

Individual judgment and group interaction: A variable perspective approach

An extension of the T. M. Ostrom and H. S. Upshaw perspective model (1968, in A. Greenwald, T. Brock, and T. Ostrom (Eds.), Psychological foundations of attitudes, New York: Academic Press) of attitudinal judgments, incorporating a subjective scale range concept, was examined in relation to the effects of group interaction on individual members' attitudinal judgments. Subjects made attitudinal judgments after reading a criminal case history and then, either individually or as members of four person groups, decided on the appropriate sentence for the criminal for two different cases. The results showed that the subjective scale range concept was useful to account for the subjects' attitudinal judgments. Further analysis showed that the group interaction provided both informational and normative influences on the individual members' judgments in different ways. These findings are discussed in terms of judgmental processes postulated by Ostrom and Upshaw.     

Teaching a Problem Solving Strategy to Inpatient Adolescents:

This study evaluated a recently developed program for teaching problem solving skills. Six inpatient adolescents received training in four general areas: Authority Figures; Peer Issues; Community Resources; and Alcohol and Drugs. The program featured response-specific feedback, modeling, self-monitoring, visual cues, positive reinforcement, response practice, self-correction, and individualized performance criterion levels. A multiple baseline across groups design was used in which each group (N + 3) received baseline, training, probes, and pre/post training generalization assessments. Generalization was assessed to two different sets of untrained problem situations that contained similar and dissimilar situations to those used in training. One set was assessed during probes and the other in pre/post evaluations. Both the probes and post assessment results revealed that the subjects' verbal problem solving skills had generalized to both types of situations. Furthermore, the subjects' three-month post assessment scores demonstrated partial maintenance and were comparable to those of a group of normal high school students. Issues related to these results and suggestions for future research are discussed.     

Extra-legal factors and product liability: The influence of mock jurors' demographic characteristics and intuitions about the cause of an injury

Two experiments were performed to investigate the role of extra-legal factors in a simulated product liability trial. In cases where the factual evidence was identical, subjects' liability judgments varied as a function of the case-specific factor of the alleged source of the plaintiffs injury. In deciding cases differently depending on the alleged cause, subjects relied on intuitions about what injury sources are more or less likely to cause a certain kind of injury. Juror-specific factors also influenced subjects' verdicts. There was no difference between students and non-students, but race and SEC—factors that are often correlated with student status—did affect subjects' verdicts. Low-SES and minority subjects were more likely to find the defendant liable than high-SES and white subjects. The results are considered in terms of general decision-making processes, and the implications for jury selection and mock jury research are discussed.     

Factor Structure of Temperament in the Third Year of Life

In two procedures, subjects were asked to perform an arithmetic task while hearing distracting auditory messages. Subjects were instructed to ignore these messages. After each trial, subjects judged how disruptive they felt that trial's distractor had been. Subjects' self-reports were unrelated to the actual distraction effect, measured in performance. In Experiment 2, a manipulation of motivation considerably decreased the auditory messages' ability to distract; this large shift in distractor potency was not reflected in subjects' self-reports. In both procedures, subjects' judgments of distraction were not random but were systematically related to parameters of message content, parameters that turned out to be irrelevant for distractor potency.     

How (far) can rationality be naturalized?

The paper shows why and how an empirical study of fast-and-frugal heuristics can provide norms of good reasoning, and thus how (and how far) rationality can be naturalized. We explain the heuristics that humans often rely on in solving problems, for example, choosing investment strategies or apartments, placing bets in sports, or making library searches. We then show that heuristics can lead to judgments that are as accurate as or even more accurate than strategies that use more information and computation, including optimization methods. A standard way to defend the use of heuristics is by reference to accuracy-effort trade-offs. We take a different route, emphasizing ecological rationality (the relationship between cognitive heuristics and environment), and argue that in uncertain environments, more information and computation are not always better (the ??less-can-be-more?? doctrine). The resulting naturalism about rationality is thus normative because it not only describes what heuristics people use, but also in which specific environments one should rely on a heuristic in order to make better inferences. While we desist from claiming that the scope of ecological rationality is unlimited, we think it is of wide practical use.     

The Effect of Incentive Structure on Heuristic Decision Making: The Proportion Heuristic1

When making judgments, individuals often utilize heuristics to interpret information. This paper reports on a series of experiments designed to test the ways in which incentive mechanisms influence the use of a particular heuristic in decision making. These experiments demonstrate how information regarding the number of available practice problems influences the behaviors of individuals preparing for an exam (the proportion heuristic). More importantly, the extent to which this information influences behavior depends critically on the way in which performance incentives are structured. In particular, relative compensation schemes magnify the influence of this heuristic, while joint compensation schemes dampen its influence. These results are discussed with respect to the literature on effective compensation.     

Heading judgments in minimal environments: the value of a heuristic when invariants are rare

Observers made systematic heading judgments in two experiments simulating their translation through an environment with only two trees. When those trees converged or decelerated apart, observers tended to follow the invariant information and make heading judgments outside the near member of the pair. When those trees accelerated apart, however, observers tended to follow the heuristic information and make judgments outside the far member, although this result was tempered by the angular separation between the trees and their relative acceleration. The simultaneous existence and use of invariants and heuristics are discussed in terms of different metatheoretical approaches to perception.