Demographic and health factors associated with enrollment in posttrial studies: the Women's Health Initiative Hormone Therapy Trials.

BackgroundAfter clinical trials end, continued follow-up of the assembled cohort often is desirable for additional research. Factors influencing participants’ decisions to consent to additional follow-up and how these shape posttrial cohorts have not been broadly studied.PurposeWe examined how two re-enrollment campaigns and the passage of time altered features of the posttrial cohorts compared with the original Women’s Health Initiative (WHI) Hormone Therapy clinical trials.MethodsWe examined associations that markers of sociodemography, health, lifestyle, and on-trial experiences had with re-enrollment and contrasted the characteristics of successive posttrial cohorts with those of the original enrollees.ResultsThe posttrial enrollment campaigns re-enrolled 81.1% and 82.5% of available women, respectively. Women who re-enrolled tended to have better health characteristics than those not re-enrolled. Compared to women of comparable age in the original cohort, women retained for the second posttrial follo...