Designing clinical trials of interventions for mobility disability: results from the lifestyle interventions and independence for elders pilot (LIFE-P) trial.
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 < or =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.
Espeland
Mark A
MA
Department of Biostatistical Sciences, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA. mespelan@wfubmc.edu
Gill
Thomas M
TM
Guralnik
Jack
J
Miller
Michael E
ME
Fielding
Roger
R
Newman
Anne B
AB
Pahor
Marco
M
D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000473:pathology* / Q000502:physiology*; D004185:Disability Evaluation; D006233:Persons with Disabilities / Q000534:rehabilitation*; D015444:Exercise; D005260:Female; D006266:Health Education; D006801:Humans; D008019:Life Style; D016014:Linear Models; D008297:Male; D010865:Pilot Projects; D016032:Randomized Controlled Trials as Topic; D012107:Research Design