Differential Attrition in Health Behaviour Change Trials: a Systematic Review and Meta-analysis

  • R. Crutzen
  • W. Viechtbauer
  • M. Spigt
  • D. Kotz


Objective: Attrition is a common problem in health behaviour change (HBC) trials. When the degree of attrition differs between treatment conditions, then this is called differential attrition and is regarded as a major threat to internal validity. The primary research question of this study was: How often and to what degree does differential attrition occur in HBC trials? Design: A systematic review and meta-analysis of a random selection of HBC trials (k=60). We meta-analysed the relative attrition rates using a random-effects model and examined the relationship between the relative attrition rates and potential moderators: the amount of human contact in delivery and the intensity of the intervention/control condition, the type of control condition, and the follow-up intensity and duration. Main Outcome Measures: Relative attrition rates. Results: The average attrition rate was 18% (SD=0.15; median=0.15) in the intervention and 17% (SD=0.13; median=0.13) in the control conditions. The estimated average relative attrition rate was 1.10 (95%CI: 1.01-1.20, p=.02), suggesting an overall higher attrition rate of 10% in intervention conditions. This relative attrition rate was not related to any of the potential moderators. Conclusion: There is indication of a slightly higher amount of attrition on average in the intervention conditions of HBC trials.