Are observational data on therapeutic outcome trustworthy?

Abstract

Randomized controlled trials have become the golden standard to assess the effectiveness of a therapeutic action. Observational studies can be used to monitor effects of routinely applied therapeutic procedures. The validity of such studies can always be questioned and the results must be assessed in light of possible sources of bias. This issue is exemplified by the analysis of more than 10,000 patients admitted for coronary artery by-pass surgery in Gothenburg early in this century.