title: Baseline participant characteristics and risk for dropout from ten obesity randomized controlled trials: a pooled analysis of individual level data.
abstract: BACKGROUND
  Understanding participant demographic characteristics that inform the optimal design of obesity RCTs have been examined in few studies. The objective of this study was to investigate the association of individual participant characteristics and dropout rates (DORs) in obesity randomized controlled trials (RCT) by pooling data from several publicly available datasets for analyses. We comprehensively characterize DORs and patterns in obesity RCTs at the individual study level, and describe how such rates and patterns vary as a function of individual-level characteristics.
  
  
  METHODS
  We obtained and analyzed nine publicly-available, obesity RCT datasets that examined weight loss or weight gain prevention as a primary or secondary endpoint. Four risk factors for dropout were examined by Cox proportional hazards including sex, age, baseline BMI, and race/ethnicity. The individual study data were pooled in the final analyses with a random effect for study, and HR and 95% CIs were computed.
  
  
  RESULTS
  Results of the multivariate analysis indicated that the risk of dropout was significantly higher for females compared to males (HR= 1.24, 95% CI = 1.05, 1.46). Hispanics and Non-Hispanic blacks had a significantly higher dropout rate compared to non-Hispanic whites (HR= 1.62, 95% CI = 1.37, 1.91; HR= 1.22, 95% CI = 1.11, 1.35, respectively). There was a significantly increased risk of dropout associated with advancing age (HR= 1.02, 95% CI = 1.01, 1.02) and increasing BMI (HR= 1.03, 95% CI = 1.03, 1.04).
  
  
  CONCLUSIONS
  As more studies may focus on special populations, researchers designing obesity RCTs may wish to oversample in certain demographic groups if attempting to match comparison groups based on generalized estimates of expected dropout rates, or otherwise adjusta prioripower estimates. Understanding true reasons for dropout may require additional methods of data gathering not generally employed in obesity RCTs, e.g. time on treatment.
authors.affiliation: Office of Energetics, School of Public Health, University of Alabama at Birmingham, Birmingham, AL, USA ; Nutrition Obesity Research Center, University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: Kaiser
authors.affiliation: Nutrition Obesity Research Center, University of Alabama at Birmingham, Birmingham, AL, USA ; Department of Epidemiology, School of Public Health, University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Olivia
authors.initials: O
authors.lastname: Affuso
authors.affiliation: Nutrition Obesity Research Center, University of Alabama at Birmingham, Birmingham, AL, USA ; Department of Preventive Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Renee
authors.initials: R
authors.lastname: Desmond
authors.affiliation: Office of Energetics, School of Public Health, University of Alabama at Birmingham, Birmingham, AL, USA ; Nutrition Obesity Research Center, University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: David B
authors.initials: DB
authors.lastname: Allison
keywords: dropout; obesity; participant characteristics; pooled analysis; randomized trials