A recent study examining predictors of participant dropout in a clinical trial of treatments for mild cognitive impairment (MCI) has found that participants recruited by NIA-funded Alzheimer's Disease Centers (ADCs) and university-affiliated sites have dramatically lower dropout rates than do those recruited by commercial sites. The authors of the study, including researchers in ADCs at the University of California, San Diego, and the Mayo Clinic, suggest that superior participant retention rates may translate into greater statistical power and validity of clinical trial results.
A high number of dropouts during a trial can weaken the statistical power of a trial and make it more difficult to detect an effect. In addition, a high number of dropouts may bias results, because participants that drop out may be different (e.g., they may be sicker, etc.) from those who complete the trial.
The Edland, et al., study identified several demographic parameters that, in addition to the trial site, predict a higher dropout rate. Some of these include marital status, education, and race/ethnicity. For example, lower education and non-white race were associated with higher dropout. The authors speculate that retention efforts targeting the identified subgroups may improve the validity and power of future trials.
The authors offer several possible causes for the differences in subject retention between ADCs and university-affiliated trial sites compared to commercial sites. The authors note that commercial sites tend to recruit more subjects through advertising. ADCs and university-affiliated sites also recruit through advertising, but they recruit many participants from their clinic populations. Longstanding relationships among clinic staff and participants may improve retention. Moreover, people who respond to advertising may be more focused on receiving the active drug or treatment and be more likely to drop out if they believe they are receiving placebo, think the drug is not working, or it causes unwelcome side effects.
Edland, S.D., et al. NIA-funded Alzheimer Centers are more efficient than commercial clinical recruitment sites for conducting secondary prevention trials of dementia. Alzheimer's Disease and Associated Disorders. 2010. 24(2):159-64.