Subject selection bias in alcoholics volunteering for a treatment study.

Baseline differences in alcoholism problem severity were compared between alcoholics who did and did not volunteer to participate in a treatment effectiveness study. A positive relationship was found between self-reports of alcohol-related problems and the degree of research participation. Group differences were also revealed in the rate of treatment completion. Possible explanations and solutions for this volunteer bias are discussed.

RCT Entities:   Population Interventions Outcomes