Use of exclusion criteria in selecting research subjects and its effect on the generalizability of alcohol treatment outcome studies

Objective: Researchers have not systematically examined how exclusion criteria used in selection of research subjects affect the generalizability of treatment outcome research. This study evaluated the use of exclusion criteria in alcohol treatment outcome research and its effects on the comparability of research subjects with real-world individuals seeking alcohol treatment. Method: Eight of the most common exclusion criteria described in the alcohol treatment research literature were operationalized and applied to large, representative clinical patient samples from the public and private sectors to determine whether the hypothetical research samples differed substantially from real-world samples. Five hundred ninety-three consecutive individuals seeking alcohol treatment at one of eight treatment programs participated. A trained research technician gathered information from participants on demographic variables and on alcohol, drug, and psychiatric problems as measured by the Addiction Severity Index. Results: Large proportions of potential research subjects were excluded under most of the criteria tested. The overall pattern of results showed that African Americans, low-income individuals, and individuals who had more severe alcohol, drug, and psychiatric problems were disproportionately excluded under most criteria. Conclusions: Exclusion criteria can result in alcohol treatment outcome research samples that are more heavily composed of white, economically stable, and higher-functioning individuals than are real-world samples of substance abuse patients seen in clinical practice, potentially compromising the generalizability of results. For both scientific and ethical reasons, in addition to studies that use exclusion criteria, outcome research that uses no or minimal exclusion criteria should be conducted so that alcohol treatment outcome research can be better generalized to vulnerable populations.