Management of Confounding in Controlled Orthopaedic Trials

Confounding occurs when the effect of an exposure on an outcome is distorted by a confounding factor and will lead to spurious effect estimates in clinical studies. Although confounding can be minimized at the design stage, residual confounding may remain. An argument therefore can be made for controlling for confounding during data analysis in all studies. We asked whether confounding is considered in controlled trials in orthopaedic research and hypothesized the likelihood of doing so is affected by participation of a scientifically trained individual and associated with the magnitude of the impact factor. We performed a cross-sectional study of all controlled trials published in 2006 in eight orthopaedic journals with a high impact factor. In 126 controlled studies, 20 (15.9%; 95% confidence interval, 9.5%–22.3%) studies discussed confounding without adjusting in the analysis. Thirty-eight (30.2%; 95% confidence interval, 22.2%–38.2%) controlled for confounding, although we suspect the true proportion might be somewhat higher. Participation of a methodologically trained researcher was associated with (odds ratio, 3.85) controlling for confounding, although there was no association between impact factor and controlling for confounding. The question remains to what extent the validity of published findings is affected by failure to control for confounding.