NIA-funded Alzheimer centers are more efficient than commercial clinical recruitment sites for conducting secondary prevention trials of dementia

Steven D. Edland, Jennifer A. Emond, Paul S. Aisen, Ronald Carl Petersen

Research output: Contribution to journalArticle

17 Scopus citations


Study participant dropout compromises clinical trials by reducing statistical power and potentially biasing findings. We use data from a trial of treatments to delay the progression of mild cognitive impairment to Alzheimer disease (AD) [NEJM 2005;352 (23):79 to 88] to determine predictors of study participant dropout and inform the design and implementation of future trials. Time to study discontinuation was modeled by proportional hazards regression with censoring at incident dementia or trial completion. Of 769 participants, 230 (30%) discontinued prematurely. Risk of dropout was higher among nonwhites [hazard ratio (HR) 2.1, P=0.0007], participants with less than college education (HR=1.6, P=0.02), participants with a Hamilton Depression score of 6 or more (HR=1.3, P=0.04), unmarried males (HR=2.1 relative to married males, P=0.003) and participants recruited by commercial clinical sites (HR=2.2 relative to participants recruited by NIA-funded AD research centers, P<0.0001). A trial using commercial sites with the discontinuation rates and incident dementia event rates experienced in this trial would require 80% more participants than a comparably powered trial using NIA-funded AD research center sites. Targeted retention efforts and utilization of academic sites could substantively improve the statistical power and validity of future clinical trials of cognitively impaired elderly.

Original languageEnglish (US)
Pages (from-to)159-164
Number of pages6
JournalAlzheimer Disease and Associated Disorders
Issue number2
StatePublished - Apr 2010



  • Attrition
  • Clinical trial methodology
  • Dropout
  • Loss to follow-up
  • Power
  • Retention
  • Sample size

ASJC Scopus subject areas

  • Geriatrics and Gerontology
  • Psychiatry and Mental health
  • Gerontology
  • Clinical Psychology

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