Three experiments show that information consistent with a preferred conclusion is examined less critically than information inconsistent with a preferred conclusion, and consequently, less information is required to reach the former than the latter. In Study 1, Ss judged which of 2 students was most intelligent, believing they would work closely with the one they chose. Ss required less information to decide that a dislikable student was less intelligent than that he was more intelligent. In Studies 2 and 3, Ss given an unfavorable medical test result took longer to decide their test result was complete, were more likely to retest the validity of their result, cited more life irregularities that might have affected test accuracy, and rated test accuracy as lower than did Ss receiving more favorable diagnoses. Results suggest that a core component of self-serving bias is the differential quantity of cognitive processing given to preference-consistent and preference-inconsistent information.
Ditto, P. H., & Lopez, D. F. (1992). Motivated skepticism: Use of differential decision criteria for preferred and nonpreferred conclusions. Journal of Personality and Social Psychology, 63(4), 568-584.