Perception of Social Distributions Richard E

Journal of Personality and Social Psychology Copyright 1985 by the American Psychological Association, Inc. 1985, Vol. 48, No. 2, 297-311 0022-3514/85/S00.75 Perception of Social Distributions Richard E. Nisbett and Ziva Kunda University of Michigan Accurate representation of the distribution of social attitudes and behaviors can guide effective social behavior and is often essential for correct inferences. We examined the accuracy of people's beliefs about the distributions of a large number of attitudinal and behavioral dimensions. In two studies we measured actual attitudes and behaviors in a student population, and we assessed beliefs by asking subjects to estimate the distribution of 100 students on these dimensions. We examined the accuracy of subjects' perceptions of the means, standard deviations, and distribution shapes. Subjects showed a number of systematic biases, including overestimation of dispersion and overestimation of the means of behavioral distributions and a false consensus bias, but their overall accuracy was impressive. Approximate knowledge of the distribu- ences about the meaning of social behavior. tions of important social variables would In fact, Kelley (1967) considered "consensus seem to be essential for effective social func- information," that is, information about the tioning. Reasonably accurate guesses about distributions of people's attitudes and behav- the dispersion and central tendency of im- ior, to be a major factor in his analysis of portant behavioral and attitudinal dimensions variance (ANOVA) scheme for inferences about could serve to guide one's behavior and self- causality in the social domain. More recently, presentation in unfamiliar social situations. Thagard and Nisbett (1982) have argued that Such knowledge could allow one to adhere knowledge about the variability of kinds of to accepted norms of behavior and conver- objects, including social objects, is re- sation and to steer away from controversial quired for appropriate generalizations. Nis- topics so as to avoid offending others who bett, Krantz, Jepson, and Kunda (1983) have hold different opinions. Indeed, one's effec- demonstrated that such knowledge mediates tiveness in group situations often depends on other types of statistical inference as well. the ability to gauge the extent of support for Despite the importance of people's percep- one's own position. Politicians have long ap- tions of social distributions, there are very preciated the value of knowledge about others' few studies that have examined the degree of opinions, and contemporary ones are willing people's accuracy in perceiving the central to spend large sums of money on polls de- tendency, dispersion, or shape of behavioral signed to obtain very precise knowledge of and attitudinal distributions. opinions. Some indirect evidence comes from work Approximate knowledge of the parameters on perception of physical objects, which in- of social distributions also would seem to be dicates that people are highly sensitive to all essential in order to make appropriate infer- three of these parameters. It has long been known that people are quite able to estimate the central tendencies of perceptual distri- This research was supported by National Science butions (e.g., Peterson & Beach, 1967; Posner Foundation Grant SES-8218846 and National Institute & Keele, 1968). More recent work by Fried of Mental Health Grant 1RO1 MH38466-01. We thank J. E. Keith Smith for advice on the analysis of the data and Holyoak (1984; Flannagan, Fried, & and Henri Zukier for theoretical suggestions. Keith Hol- Holyoak, 1984) shows that people are also yoak, Daniel Kahneman, Jon Krosnick, Darrin Lehman, sensitive to dispersion and distribution shape. and Lee Ross provided thoughtful criticism of an earlier They presented subjects with computer-gen- draft of this article. Sara Freeland provided able editorial help. erated variations on a particular visual theme, Requests for reprints should be sent to Richard E. for example, a pattern of light and dark Nisbett, Institute for Social Research, University of Mich- patches on a grid or a pattern of colored igan, Ann Arbor, Michigan 48106. rectangles. 297 298 RICHARD E. NISBETT AND ZIVA KUNDA Subjects were more willing to classify a subject to some unique sources of bias. The given variant as an exemplar of a particular following potential errors in the perception type of pattern if the previous exemplars were of social distributions have been identified highly variable on the dimensions composing (cf. Nisbett & Ross, 1980): the type, than if previous exemplars were less 1. People seem likely to be influenced by variable. Subjects were also highly sensitive the availability of exemplars (Tversky & to distribution type. When the dimensions Kahneman, 1973). Because extreme behaviors from which exemplars were constructed were and opinions are likely to be salient (indeed distributed in a normal bell-shaped curve, people with extreme dispositions and opinions subjects readily learned to classify a pattern are likely to take steps to guarantee that they as being of the particular type that in fact will be salient), their overrepresentation in generated it. The probability of assigning a memory may lead to an overestimation of pattern to its parent type was greatest near the variability of social distributions. Indeed, the center of the dimensions underlying the it has been shown that individuals with ex- type and fell off in proportions dictated by treme physical or social characteristics are the shape of the normal curve. more available in memory and are conse- When subjects were instead presented with quently estimated as more frequent than cor- patterns generated by bimodal, U-shaped di- responding numbers of less extreme individ- mensions, their classifications did not track uals (Rothbart, Fulero, Jensen, Howard, & the actual frequencies of the dimension values. Birrell, 1978). Instead, subjects made their guesses about 2. A special case of availability, that is, classification as if they believed the distribu- knowledge about one's own value on social tions of the dimensions were normal. Even dimensions, might produce systematic errors after a very large number of trials exposing in estimates of central tendency. One's per- them to different patterns, subjects failed to ception of the entire distribution might be distribute their guesses in the same fashion shifted toward one's own location. This false as the actual dimensions. Instead, their guesses consensus tendency has already been docu- were distributed in an essentially flat fashion mented for a number of attitudes (e.g. Fields across the dimensions. & Schuman, 1976) and behaviors (Ross, Work on the perception of physical dimen- Greene, & House, 1977). sions thus indicates that people can be quite These investigators and others whom they accurate in assessing central tendency and cite (as well as subsequent studies, e.g., Judd dispersion and that they have a very heavy & Johnson, 1981 and van der Pligt, 1984), bias toward perceiving normality in distri- have shown that people tend to assume that bution shapes. Given the apparent frequency a higher fraction of the population shares of normal distributions in nature, it is possible their own views, or would behave as they that this bias might serve to make perception have, than is the case. The work gives us little more accurate and efficient. Observation of indication, however, of the degree of distortion a very few exemplars would serve to give a that this produces in estimates of central fair idea of central tendency, and, if normality tendency and no indication at all of the of the dimensions is presumed, variance or effects on estimates of dispersion or distri- standard deviation could also be estimated bution shape. with fair accuracy. Thus the classification of 3. There is a well-known tendency of group new objects or events would be maximally members to exaggerate the differences be- efficient in a statistical sense, so long as the tween themselves and out-group members underlying dimensions are in fact distributed (e.g., Campbell, 1967; Child & Doob, 1943; approximately normally. Quattrone, in press; Sherif, Harvey, White, Although it is possible that people are also Hood, & Sherif, 1961; Tajfel, 1970; Vinacke, accurate about the central tendency and dis- 1949). This suggests the possibility that people persion of social distributions and have a might have a bias toward assuming bimodality useful bias toward assuming their normality, for social distributions—"my kind" and "not there are good grounds for suspecting that my kind" (a tendency actually found in one they might not be very accurate. This is study by Judd & Johnson, 1981). because beliefs about social dimensions are Current theory and some evidence therefore SOCIAL DISTRIBUTIONS 299 suggest that people may not be as accurate that beliefs about social distributions might in their perceptions of statistical parameters be quite inaccurate, perhaps due to the kinds for social distributions as in their perceptions of biases discussed earlier. for physical distributions. Additional support Thus it is important to determine how for this expectation is suggested by research accurate people's perceptions of social distri- on inferential errors. Substantial evidence butions are, both because of the "first order" shows that people do not make proper infer- importance of accuracy about social distri- ences when reasoning about problems involv- butions for purposes of social

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