Objective: To determine to what extent the substance-use information obtained in surveys is affected by method of data collection.
Study design and setting: Questions on the use of alcohol and drugs were administered to samples of Minnesota adults assigned to one of two conditions to test the effect of mode of administration (mail and telephone); 816 persons completed the survey, roughly one half by mail and one half by telephone.
Results: Those interviewed by telephone revealed more heavy use of alcohol, but the mail sample includes disproportionate numbers of respondents from demographic groups that exhibit less use. Controlling for these differences across modes, as well as the differential use of listed telephone numbers and addresses, reduces the effect of mode on one measure of heavy alcohol use to nonsignificance but yields significant effects of mode on others. Specifically, those in the mail condition reported higher levels of illicit drug use in the last year, alcohol use in the last month, and heavy alcohol use in the last 2 weeks.
Conclusions: The greater, and arguably more accurate, reporting of substance use, coupled with potential cost savings, suggests that researchers should consider using mail surveys for investigating substance use.