Illusory correlation and attitude-based vested interest

The present studies test whether having a ‘vested interest’ in a particular outcome affects perceived covariation. Vested interest was defined as a function of whether Dutch university students were in favour or against the implementation of a threatening policy (receiving lectures in English as opposed to the native Dutch). In both studies subjects were told that this policy would be tried out at either their own or another comparable university, and that the university chosen would be the one with the greatest proportion of support for the plan. In Study 1 subjects (n = 151) were presented with statements expressing pro or contra attitudes and arguments to the policy. These were ostensibly derived from students at both universities but university affiliation was not indicated. In Study 2 (n = 114) similar information was provided but the statements were attributed to students from the two universities, such that there was an equal proportion of opposition/support for the plan at both universities. We hypothesized that illusory correlations would reflect the vested interest of attitude such that students opposing the policy would overestimate the proportion of opponents to supporters at their own university compared to those in favour of the policy. The results of both studies supported our hypothesis and they also revealed attitude to be a more important predictor of illusory correlation than perceived personal consequences for themselves. The prediction that illusory correlations would be weaker in Study 2 than in Study 1, because it provides less scope for bias, was not supported. The implications of these findings are discussed.