Cohort maintenance and comparability in a pharmacoepidemiologic study using a commercial consumer panel to recruit comparators.

The Upjohn Consumer Health Survey (UCHS) was a prospective, observational study of users of ROGAINE (REGAINE in international markets) Topical Solution 2% (N=11,122) and a Comparator cohort (N=11,173) which was selected and group matched by stratified random sampling from among members of a commercial consumer panel. Study endpoints were confirmed cause-specific deaths and hospitalizations within 12 months of study entry. Data collection was accomplished by participant interviews and confirmation of participant-reported medical events. At least 94% of both cohorts completed 12 months of follow-up, with the completion rate highest in the Comparator cohort (96.8%). Although successful matching was achieved on the demographic variables used to select the Comparators, members of the two cohorts differed significantly in the presence of baseline chronic medical conditions and other risk factors for study endpoints. A commercial consumer panel is valuable for rapid selection of demographically-matched comparators for targeted cohorts which continue in the study through long-term follow-up. Multi-stage sampling may need to be employed when more specific characteristics must be identified.