Population reach and recruitment bias in a maintenance RCT in physically active older adults

Brian C. Martinson, A. Lauren Crain, Nancy E. Sherwood, Marcia G. Hayes, Nicolaas P. Pronk, Patrick J. O'Connor

Research output: Contribution to journalArticlepeer-review

37 Scopus citations


Objective: To assess the representativeness of older adults recruited to a physical activity maintenance RCT by conducting sequential comparisons to characterize study sample composition changes occurring between sampling frame construction and study enrollment. Method: Study subjects (N = 1049) were 50 to 70 year old men and women who had increased physical activity within the past year recruited from a Midwestern managed care organization. Results: Those responding to an initial mailed screener differed on demographic, behavioral, and SES characteristics from those not responding. Compared with ineligibles, eligible individuals were signifcantly younger, more highly educated, and more likely to report improved health in the prior year. Compared with eligible individuals who did not enroll, enrollees had generally higher education and income. Conclusions: Physical activity promotion programs in older adults may have limited reach and substantial volunteer bias. Additional strategies to increase the reach of physical activity interventions into the target population are needed.

Original languageEnglish (US)
Pages (from-to)127-135
Number of pages9
JournalJournal of Physical Activity and Health
Issue number1
StatePublished - Jan 2010


  • Health maintenance organizations
  • Intervention studies
  • Motor activity
  • Randomized controlled trial
  • Research subject recruitment
  • Selection bias

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