Addictive Behaviors, Vol. 25, No. 5, pp. 785–790, 2000 Copyright © 2000 Elsevier Science Ltd. Printed in the USA. All rights reserved 0306-4603/00/$–see front matter PII S0306-4603(00)00064-2 785 Pergamon BRIEF REPORT CHARACTERISTICS OF RESEARCH VOLUNTEERS FOR INPATIENT COCAINE STUDIES: FOCUS ON SELECTION BIAS MEHMET SOFUOGLU, SUSAN DUDISH-POULSEN, KRISTIN K. NICODEMUS, DAVID A. BABB, and DOROTHY K. HATSUKAMI University of Minnesota Abstract — In order to investigate the selection bias of subjects for inpatient human cocaine studies, characteristics of 859 potential subjects were examined. Excluded subjects compared with accepted group were more likely to be single and male, currently use drugs other than co- caine, have a history of intravenous cocaine use, and have medical or mental health problems or physical complaints. Subjects who were accepted but did not participate, compared with participants, were likely to spend more money on cocaine. These results suggest that potential subjects who were accepted to our research studies may not accurately represent all potential subjects for several important subject characteristics. © 2000 Elsevier Science Ltd. Key Words. Cocaine, Crack-cocaine, Research subjects, Selection bias. Selection bias of research subjects is important in determining the generalizability of the results from clinical trials. For drug addiction research that uses nontreatment- seeking research volunteers, selection bias is further complicated. The goal of this study was to address two related questions by comparing the outcome of phone screening of potential subjects for inpatient cocaine studies. The first question was whether the characteristics of subjects who were accepted to our studies were different than the characteristics of those who were excluded. Since the results obtained from study participants are generalized to all cocaine users, it was important to understand the differences between these two groups. The second question was whether the char- acteristics of subjects who participated in our studies were different than the charac- teristics of those who were accepted but did not participate (nonparticipants). This comparison would address whether there was a self-selection bias in addition to our selection bias. This study will extend the previous studies that investigated the charac- teristics of research subjects for inpatient cocaine studies (Dudish & Hatsukami, 1996; Foltin, Fischman, Cornell, & Butler, 1996; Lexau, Nelson, & Hatsukami, 1998; Schuster & Fischman, 1985). This research was supported by grants from National Institute on Drug Abuse (P-50 DA09259) and from the National Center for Research Resources (MO1-RR00400). We would like to thank Robin L. Bliss for statistical analysis and Clair Wilcox for preparing the manuscript. Requests for reprints should be sent to Mehmet Sofuoglu, Department of Psychiatry, University of Minnesota, Box 392 UMHC, Minneapolis, MN 55455; E-mail: sofuo001@tc.umn.edu