Does substance use affect reliabilities of the Implicit Association Test?

The authors examined whether use of alcohol or marijuana affected reliability of the Implicit Association Test (IAT; A. G. Greenwald, D. E. McGhee, & J. L. K. Schwartz, 1998). Consistent with research indicating the possibility that marijuana use depletes cognitive resources, the authors found worse reliabilities for participants who recently used marijuana than for those who had not. Recent alcohol users and nonusers demonstrated similar IAT reliability. Subsequent analyses indicated that reliability differences between marijuana users and nonusers were most pronounced when participants began with incongruous tasks and then switched to congruous tasks. Results were consistent with work on the residual costs of task switching that indicates that effortful tasks promote interference with tasks that follow. The authors discussed results in terms of IAT scoring procedures and the prevalence of use of alcohol and marijuana on university campuses.