A systematic review reveals that the credibility of subgroup claims in low back pain trials was low

Objectives To assess the credibility of subgroup claims in back pain randomized controlled trials. Study Design and Setting A sample of reports of back pain trials from 2000 to 2015 that provided a subgroup claim were included (n = 38). Two reviewers independently assessed risk of bias and credibility of subgroup claims as well as the strength of the author's claim. The credibility of subgroup claims was assessed using a 10-criteria tool, and strength of the subgroup claims was assessed based on seven criteria to categorize claims into a reasonably strong claim of a definitive subgroup effect or a more cautious claim of a possible effect. Results A total of 91 claims of a subgroup effect were reported in the 38 included trials, of which 28 were considered strong claims of a definitive effect, and 63 were cautious claims of a possible effect. None of the subgroup claims met all 10 credibility criteria, and only 24% (22 claims) satisfied at least five criteria. The only criteria satisfied by more than 50% of the claims were if the subgroup variable was a characteristic measured at baseline, and whether the test of interaction was significant. All other criteria were satisfied by less than 30% of the claims. There was no association between the credibility of subgroup claims and the journal impact factor, risk of bias, sample size, or year of publication. Conclusion The credibility of subgroup claims in back pain trials is usually low, irrespective of the strength of the authors’ claim.