Improving the evidence-base in surgery: evaluating surgical effectiveness.

This second of two articles about clinical epidemiology reviews the generation and synthesis of evidence for the effectiveness of surgical procedures. While well-designed randomized controlled trials of surgical procedures are considered the 'gold standard' of evaluation design, they may achieve high internal validity at the expense of external validity (generalizability). Improving the -evidence-base in surgery likely will require a comprehensive approach to surgical outcomes assessment, involving both improvements in the quality and quantity of randomized controlled trials as well as recognition of the complementary role of alternate study designs.