title: Designing clinical trials of interventions for mobility disability: results from the lifestyle interventions and independence for elders pilot (LIFE-P) trial.
abstract: 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.
authors.affiliation: Department of Biostatistical Sciences, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA. mespelan@wfubmc.edu
authors.forename: Mark A
authors.initials: MA
authors.lastname: Espeland
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Gill
authors.forename: Jack
authors.initials: J
authors.lastname: Guralnik
authors.forename: Michael E
authors.initials: ME
authors.lastname: Miller
authors.forename: Roger
authors.initials: R
authors.lastname: Fielding
authors.forename: Anne B
authors.initials: AB
authors.lastname: Newman
authors.forename: Marco
authors.initials: M
authors.lastname: Pahor
mesh_terms: 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