Issues in extrapolating from clinical trials to clinical practice and outcomes

Extrapolation of clinical trial results to clinical practice requires consideration of whether the trial patients were representative of clinical practice, whether the trial therapy studied was optimal, whether the sample size was adequate, and the impact of adjunctive treatments. In thrombolytic trials in particular, regional variations in attitudes to coronary angiography may have affected outcomes. Clinical trial results need to be interpreted in the light of the cost effectiveness of the application. The assessment of clinical outcomes depends on interplay between the structure and process of care, patient factors and chance. Large standardised databases are necessary to assess clinical practice and outcomes.