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Designing Clinical Trials of Interventions for Mobility Disability: Results From the Lifestyle Interventions and Independence for Elders Pilot (LIFE-P) Trial

¹ Department of Biostatistical Sciences, Wake Forest University School of Medicine, Winston-Salem, North Carolina.
² Department of Medicine, Yale University School of Medicine, New Haven, Connecticut.
³ Epidemiology and Demography Section, National Institute on Aging, Bethesda, Maryland.
⁴ Nutrition, Exercise, Physiology, and Sarcopenia Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Boston, Massachusetts.
⁵ Departments of Epidemiology and Medicine, Graduate School of Public Health, University of Pittsburgh, Pennsylvania.
⁶ Department of Aging and Geriatric Research, University of Florida, Gainesville.

Address correspondence to Mark A. Espeland, PhD, Department of Biostatistical Sciences, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157. E-mail: mespelan{at}wfubmc.edu

Background. Clinical trials to assess interventions for mobility disability are critically needed; however, data for efficiently designing such trials are lacking.

Methods. Results are described from a pilot clinical trial in which 424 volunteers aged 70–89 years were randomly assigned to one of two interventions—physical activity or a healthy aging education program—and followed for a planned minimum of 12 months. We evaluated the longitudinal distributions of four standardized outcomes to contrast how they may serve as primary outcomes of future clinical trials: ability to walk 400 meters, ability to walk 4 meters in 10 seconds, a physical performance battery, and a questionnaire focused on physical function.

Results. Changes in all four outcomes were interrelated over time. The ability to walk 400 meters as a dichotomous outcome provided the smallest sample size projections (i.e., appeared to be the most efficient outcome). It loaded most heavily on the underlying latent variable in structural equation modeling with a weight of 80%. A 4-year trial based on the outcome of the 400-meter walk is projected to require N = 962–2234 to detect an intervention effect of 30%–20% with 90% power.

Conclusions. Future clinical trials of interventions designed to influence mobility disability may have greater efficiency if they adopt the ability to complete a 400-meter walk as their primary outcome.

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