The comparison of the outcomes of different surgical techniques is the foundation of progress in cardiac surgery. Still, estimating treatment effects is a complex methodological challenge.
Randomized trials have low risk of bias but limited external validity. On the other hand, observational studies have a higher risk of bias and confounders but are more representative of clinical practice. While in theory biases may lead to an overestimation of the treatment effect in observational studies and the lower external validity may reduce the treatment effect in randomized trials, it has been reported that in other fields the estimates of treatment effects are qualitatively and quantitively similar between the two.1 Although no data specific to cardiac surgery exist, we believe that this concordance does not hold true for cardiac surgery studies (and probably for surgical studies in general).