Misuse of baseline comparison tests and subgroup analyses in surgical trials.

It is unclear whether the misuse of statistical tests that compare patients' baseline characteristics and subgroup analyses in randomized controlled trials can be extrapolated to the surgical literature. We did an observational study evaluating the current use of baseline comparability tests and subgroup analyses in surgical randomized controlled trials. Published surgical randomized controlled trials in four medical journals were identified. We also identified randomized controlled trials in the Journal of Bone and Joint Surgery (American and British volumes). We identified 72 randomized controlled trials, with a mean of 10 +/- 8 baseline variables. Of 166 significance tests, 17 (10%) were significant. Twenty-seven (38%) trials included 54 subgroup analyses with a minimum of one and maximum of 23 subgroup analyses per study. Inappropriate emphasis on subgroup analyses occurred frequently. Forty-nine (91%) analyses were performed post hoc without prior hypotheses. Investigators reported differences between subgroups in 31 (57%) of the analyses, all of which were featured in the summary or conclusion. These inferences may be misleading, making their application to clinical practice unwarranted.