Illusory Correlation

An illusory correlation occurs when a person perceives a relationship between two variables that are not in fact correlated. In the first study to demonstrate this phenomenon, participants were presented with pairs of words from two stimulus lists. Each word from the first list was paired an equal number of times with each word from the second list. Later, when participants were asked to estimate the number of times words from each of the two lists had been paired together, they consistently overestimated the number of pairings that had occurred between (a) pairs of words that differed visually from the others (i.e., unusually long words) and (b) pairs of words that shared some semantic association (e.g., lion and tiger). Thus, although all pairs occurred equally often, people gave higher frequency estimates for certain types of word pairs.

Illusory CorrelationThe importance of this bias for social psychology concerns its role in stereotyping. Historically, stereotypes were believed to result from defective personality types or were based on overgeneralization of some kernel of truth that existed in the world. Illusory correlation studies provided another basis of stereotyping by suggesting that people might form a stereotype about a group simply as a by-product of the way their minds normally process information about the world.

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In a study to test this hypothesis, researchers presented participants with a series of statements about members of two groups, Group A and Group B. The statements described members of the groups performing desirable (e.g., “John, a member of Group A, visited a sick friend in the hospital”) or undesirable (e.g., “John, a member of Group A, always talks about himself and his problems”) behaviors. Each participant read 18 desirable statements and 8 undesirable statements about members of Group A and 9 desirable statements and 4 undesirable statements about members of Group B. The total number of statements about Group A was double that of Group B (i.e., 26 statements vs. 13 statements), but the ratio of desirable to undesirable statements was identical for both groups (i.e., 18 desirable and 8 undesirable vs. 9 desirable and 4 undesirable).

Because membership in Group B and the undesirable statements were the two less frequent occurrences (like the pairs of longer words in the original research), they were more noticeable. Later, participants overestimated the number of times they had read about a member of Group B doing something undesirable. Moreover, participants also rated Group B less favorably than they did Group A. Thus, people perceived a relationship that didn’t exist in what they read.

In another experiment, desirable behaviors were used as the novel social occurrence. Participants again read statements about Group A and Group B. However, this time both groups performed more undesirable than desirable behaviors (i.e., Group A: 16 undesirable and 8 desirable; Group B: 8 undesirable and 4 desirable). Again, the ratio of desirable to undesirable statements was the same for both groups. When asked to estimate how many undesirable versus desirable behaviors members of both groups had performed, participants consistently overestimated the frequency of members of the smaller group (i.e., Group B) performing the less frequent behavior (i.e., desirable behavior). Consequently, in this study, Group B was rated more favorably than Group A.

Although evaluatively equivalent information was provided about both groups, people perceived the groups differently because of the effect of distinctive information. This is known as a distinctiveness-based illusory correlation because a relationship is believed to exist between two variables as the result of the special attention given to distinctive (i.e., infrequent) information.

Expectancy-based illusory correlations are misperceptions of relationships due to people’s preexisting expectations. They provide an explanation for how stereotypes are perpetuated based on an individual’s preexisting belief about a group. They are often studied using similar techniques to those found in distinctiveness-based illusory correlation research.

In one experiment, participants read sentences describing people with different occupations. Each of the sentences described a person with a trait word that was stereotypic of the occupation (e.g., a helpful doctor, a busy waitress) or neutral (e.g., a humorous doctor, a humorous waitress). All of the adjectives were paired with all of the occupations an equal number of times. Yet when participants were asked to estimate the number of times each pairing occurred, they consistently overestimated the number of times that the stereotypic-traits had been paired with their corresponding occupations. The effect is known as an expectancy-based illusory correlation because people’s stereotypic expectancies about certain occupations lead them to perceive a relationship where none actually exists.

Alternative theories have been provided to explain why illusory correlations occur. One alternative suggests that research participants are motivated to make sense out of information they receive during a study. Because participants receive information about individuals from two different groups, the participants may assume that some difference must exist between the groups. The participants’ attempts to distinguish between the two groups produce different evaluations. Another theory proposes that illusory correlations are due to information loss. Participants are not able to remember all of the information presented about the groups; however, because they learn more information about the larger group, they remember more information about this group when asked to make an evaluation about it later. Because they remember more information about the larger group and the majority of the information they remember is positive, participants evaluate the larger groups more favorably. Similarly, another explanation suggests that illusory correlations occur not because pairings of infrequent occurrences are more distinctive but rather because information about the most common pairings (i.e., larger group with the more frequent behaviors) is so easy to recall.

The findings from both distinctiveness-based and expectancy-based illusory correlation studies are important because they demonstrate how a perceptual bias can result from normally functioning cognitive mechanisms. When this research was first reported, it challenged the then-conventional beliefs that stereotypes were the result of individual personality syndromes or that they were derived from an underlying reality. Distinctiveness-based illusory correlation research demonstrates how stereotypes are constructed by the everyday cognitive mechanisms that are constantly operating within the human mind. Similarly, research on expectancy-based illusory correlations demonstrates how stereotypic beliefs are perpetuated through the biased processing of information when it is guided by a perceiver’s prior beliefs.


  1. Hamilton, D. L., & Gifford, R. K. (1976). Illusory correlation in interpersonal perception: A cognitive basis of stereotypic judgments. Journal of Experimental .Social Psychology, 12, 392-107.
  2. Hamilton, D. L., & Rose, T. L. (1980). Illusory correlation and the maintenance of stereotypical beliefs. Journal of Personality and Social Psychology, 39, 832-845.
  3. Stroessner, S. J., & Plaks, J. E. (2001). Illusory correlation and stereotype formation: Tracing the arc of research over a quarter century. In G. B. Moskovitz (Ed.), Cognitive social psychology: The Princeton Symposium on the legacy and future of social cognition (pp. 247-259). Mahwah, NJ: Erlbaum.