Regression to the mean: implications for clinical trials of psychotropic agents in dementia

Abstract

Effective drug development depends on understanding and optimizing results from controlled clinical trials. A recent double-blind, randomized, controlled trial of the treatment of agitation in patients with Alzheimer's disease (AD) found no difference among the four arms of the study: haloperidol, trazodone, behavioral therapy, placebo. The current analysis was undertaken to further investigate the issues bearing on this outcome and to identify better means of detecting psychotropic effects in trials involving patients with AD. This was post hoc analysis of a clinical trial data set. Patients in the placebo group were divided into responders (25% reduction in symptoms), worseners (25% worsening in baseline agitation scores), and those without a change in symptoms. Analysis of the trial outcomes demonstrated that the reduction observed in the placebo group was of the same magnitude as predicted by regression to the mean. Patients exhibiting greater improvement had more severe baseline behavioral disturbances. The relatively modest severity of agitation and the low medication doses achieved in the study may have further contributed to the failure to distinguish among treatment groups. Research design adjustments such as collection of both screening and baseline measures to determine eligibility may limit the effects of regression to the mean on trial outcomes and reduce this challenge to clinical trials.