title: Statistical analysis of efficacy in falls prevention trials.
abstract: BACKGROUND
  Many different and sometimes inappropriate statistical techniques have been used to analyze the results of randomized controlled trials of falls prevention programs for elderly people. This makes comparison of the efficacy of particular interventions difficult.
  
  
  METHODS
  We used raw data from two randomized controlled trials of a home exercise program to compare the number of falls in the exercise and control groups during the trials. We developed two different survival analysis models (Andersen-Gill and marginal Cox regression) and a negative binomial regression model for each trial. These techniques a) allow for the fact that falls are frequent, recurrent events with a non-normal distribution; b) adjust for the follow-up time of individual participants; and c) allow the addition of covariates.
  
  
  RESULTS
  In one trial, the three different statistical techniques gave surprisingly similar results for the efficacy of the intervention but, in a second trial, underlying assumptions were violated for the two Cox regression models. Negative binomial regression models were easier to use.
  
  
  CONCLUSIONS
  We recommend negative binomial regression models for evaluating the efficacy of falls prevention programs.
authors.affiliation: Department of Medical and Surgical Sciences, University of Otago Medical School, P.O. Box 913, Dunedin, New Zealand. clare.robertson@stonebow.otago.ac.nz
authors.forename: M Clare
authors.initials: MC
authors.lastname: Robertson
authors.forename: A John
authors.initials: AJ
authors.lastname: Campbell
authors.forename: Peter
authors.initials: P
authors.lastname: Herbison
mesh_terms: D000058:Accidental Falls / Q000517:prevention & control*; D000368:Aged; D000369:Aged, 80 and over; D015986:Confounding Factors, Epidemiologic; D005081:Exercise Therapy / Q000706:statistics & numerical data; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D016013:Likelihood Functions; D008297:Male; D015233:Models, Statistical; D016016:Proportional Hazards Models; D012044:Regression Analysis; D016019:Survival Analysis; D016896:Treatment Outcome