Evaluation of Enrollment Bias in a Physical-Activity-Promotion Program for Seniors

Health-promotion programs’ success depends on their ability to enroll representative samples of the target population, particularly those who are hard to reach and those who can benefit the most from such programs. This article evaluates enrollment bias in the recruitment process, examines the usefulness of a 2-phased recruitment strategy in enrolling representative proportions of eligible individuals in a physical-activity-promotion program for older adults, and explores predictors of enrollment. Of 1,381 randomly selected Medicare HMO members. 519 were eligible. Of these, 54% attended an informational meeting and 33% enrolled in the program. Relative to the target population, a representative proportion of women was enrolled, but those who enrolled were slightly younger. Of those who were eligible, a representative proportion of sedentary participants was recruited, those who were overweight were overrep-resented, and the oldest old, less educated, ethnic minorities, and precontem-plators of physical activity were underrepresented. Modifiable predictors of enrollment included interest in health, previous health-class attendance, and having had a physician recommend exercise.