David A. Kenny
March 29, 2021

Chapter 7 of Interpersonal Perception: The Foundation of Social Relationships. See especially pages 222-225.

Assumed similarity is the degree to which a perceiver sees him or herself, he or she sees others the same way. Using the Social Relations Model, assumed similarity is assessed by the correlation between self-perception and the perceiver effect.  So if Jane sees others friendly, does Jane see herself as friendly.  Using Laing notation, it is symbolized as A(B) = A(A).  

The topic of assumed similarity has a long history and has been given many different names, including false consensus bias, projection, attributive projection, social projection, the self-based heuristic, and self-anchoring.

In 1931, Daniel Katz, Floyd Allport, and Margaret Jenness found that students who admitted to cheating on exams thought that cheating was much more common than students who did not cheat on exams. Assumed similarity was a key question in the pre-Cronbach years of research on interpersonal perception. Lee Cronbach’s classic 1955 paper took aim at questioning the measurement of assumed similarity, as well as accuracy, with “assumed similarity” being in the title of that paper. The major focus of this line of work was that assumed similarity was a bias that needed to be controlled in the measurement of accuracy.

Most of the more modern work on assumed similarity is on what was called by Lee Ross and colleagues in 1977 false consensus bias. Likely part of the interest in false consensus bias was that it could be studied by looking at individuals and did not require dyads or groups. To study false consensus bias, researchers examined those who had different opinions (e.g., liking liver), and each participant guessed the percentage of persons who agreed with him or her. The finding is that, if a person liked liver, he or she was more likely to believe that others also liked liver than if he or she did not like liver. Calling it a bias would seem to imply that assumed similarity was an error. However, this is not necessarily the case. Beginning with Robyn Dawes in 1989 and extended by Joachim Krueger and Russell Clement in 1994, it was demonstrated that false consensus bias could lead to accuracy. By assuming that another is similar, perceivers can become more accurate in predicting the other.

More recently, Edward Lemay of the University of Maryland has studied what he calls projection in close relationships. For instance in 2007, he, Margaret Clark, and Brooke Feeney measured how people project their responsiveness to needs onto partners.

Dustin Wood and his colleagues in 2010, across three studies with over 500 participants, found a somewhat lower value of assumed similarity, .17, than other–other similarity, .19. In a larger meta-analysis in 2010, Tessa West and I found that the relationship of self-perception with the perception of one other to be .25. Note that average level of assimilation, other–other similarity, was .27, a value that is statistically greater than the .25 value of assumed similarity. Thus perceivers assume slightly more similarity of others than they do between themselves and others.

Hughes and colleagues (2021) developed an elaborate model for assumed similarity, using ideas initially proposed by Campbell et al. (1964). They proposed that assumed similarity might be a bias or perception or it might be based on the reality of the interaction partner's actual behavior, what they called perceiver-induced similarity. They found support for their hypothesis.

There has been much less interest in factors that increase or decrease assumed similarity than there has been for self–other agreement. In 2010, Tessa West and I explored which factors lead to greater assumed similarity and additionally asked whether the factor was more or less important in explaining assimilation. We did find that traits that were more visible showed less assumed similarity. Additionally, there was evidence that when perceivers evaluated more targets, they assumed greater similarity than when they evaluated fewer targets. This latter effect was stronger for assumed similarity than it was for assimilation.

The most studied moderator of assumed similarity is whether the targets are members of the perceiver’s ingroup or comprise an outgroup. The hypothesis is that there is more assumed similarity when others are ingroup members than when they are outgroup members. This hypothesis has been confirmed in a meta-analysis of the false consensus bias literature in 2005 by Jordan Robbins and Joachim Krueger. Interestingly, there is still some assumed similarity even of outgroup members. It should also be mentioned that people who are more communal (i.e., are willing to benefit others without expecting compensation) are more likely to assume similarity (see the 2012 paper by Kenneth Locke and colleagues and the 2014 paper by Catherine Ott-Holland and colleagues).

Quite surprisingly, there is yet to be a test of greater assumed similarity for ingroup versus outgroup members using the SRM. However, I reexamined a study by Alecia Santuzzi from 2007, in which she studied groups of smokers and nonsmokers, where smoking was the topic of a group discussion. Her results show that for ingroups (smokers judging smokers, and nonsmokers judging nonsmokers), the level of assumed similarity was very high, .77, whereas for outgroup judgments (smokers judging nonsmokers and nonsmokers judging smokers), the correlation was only .12. The results show a willingness to assume similarity for ingroup members, but not for outgroup members.

Campbell, D. T., Miller, N., Lubetsky, J., & O’Connell, E. J. (1964).
Varieties of projection in trait attribution. Psychological Monographs,
78, 1–33.

Cronbach, L. (1955). Processes affecting scores on "understanding of others" and "assumed similarity." Psychological Bulletin, 52, 177-193.

Dawes, R.  M. (1989). Statistical criteria for establishing a truly false consensus effect.  Journal of Experimental Social Psychology, 25, 1-17.

Hughes, B. T., Flournoy, J., & Srivastava, S. (2021). Is perceived similarity more than assumed similarity? An interpersonal path to seeing similarity between self and others. Journal of Personality and Social Psychology, 121, 184–200.

Katz, D., Allport, F., & Jenness, M. B.  (1931). Student attitudes: A report of the Syracuse University Reaction Study. New York: Craftsman Press.

Kenny, D. A., & West, T. V. (2010). Similarity and agreement in self- and other perception: A meta-analysis. Personality and Social Psychology Review, 14, 196-213.

Krueger, J., & Clement, R. W. (1994). The truly false consensus effect: An ineradicable and egocentric bias in social perception. Journal of Personality and Social Psychology, 67, 596‑610.

Lemay, E. P., Clark, M. S., & Feeney, B. C. (2007). Projection of responsiveness to needs and the construction of satisfying communal relationships. Journal of
Personality and Social Psychology, 92, 834–853.

Locke, K. D., Craig T., Baik, K. D., & Gohil K. (2012).  Binds and bounds of communion: effects of interpersonal values on assumed similarity of self and others. Journal of Personality and Social Psychology, 103, 879-97.

Ott-Holland, C. J., Huang, J. L., Ryan, A. M., Elizondo, F., & Wadlington, P. L. (2014).  The effects of culture and gender on perceived self-other similarity in personality. Journal of Research in Personality, 53, 13-21.

Robbins, J. M., & Krueger, J. I. (2005). Social projection to ingroups and outgroups: A review and meta-analysis.  Personality and Social Psychology Review, 9, 32-47.

Ross, L., Greene, D., & House, P.  (1977). The false consensus effect: An egocentric bias in social perception and attribution processes.  Journal of Experimental Social Psychology, 13, 279–301.

Santuzzi, A. M. (2007). Perceptions and metaperceptions of negative evaluation: Group composition and interpersonal accuracy in a social relations model. Group Processes and Intergroup Relations, 10, 383-398.

Wood, D., Harms, P., & Vazire, S. (2010). Perceiver effects as projective tests:  What your perceptions of others say about you. Journal of Personality and Social Psychology, 99, 174–190.


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