Responder analyses in randomised controlled trials for chronic low back pain: an overview of currently used methods.

PURPOSE: To provide an overview and a critical appraisal of the use of responder analyses in published randomised controlled trials (RCTs) of interventions for chronic low back pain (LBP). The methodology used for the analyses, including the justification, as well as the implications of responder analyses on the conclusions was explored.
METHODS: A convenience sample of four systematic reviews evaluating 162 RCTs of interventions for chronic LBP was used to identify individual trials. Randomised trials were screened by two reviewers and included if they performed and reported a responder analysis (i.e. the proportion of participants achieving a pre-defined level of improvement). The cutoff value for responders, the period of follow-up, and the outcome measure used were extracted. Information on how RCT authors justified the methodology of their responder analyses was also appraised.
RESULTS: Twenty-eight articles (17%) using 20 different definitions of responders were included in this appraisal. Justification for the definition of responders was absent in 80% of the articles. Pain was the most frequently used domain for the definition of response (50%), followed by back-specific function (30%) and a combination of pain and function (20%). A reduction in pain intensity ≥50% was the most common threshold used to define responders (IQR 33-60%).
CONCLUSIONS: Few RCTs of interventions for chronic LBP report responder analyses. Where responder analyses are used, the methods are inconsistent. When performing responder analyses authors are encouraged to follow the recommended guidelines, using empirically derived cutoffs, and present results alongside mean differences.