This article provides a critical overview of problem-based learning (PBL), its effectiveness for knowledge acquisition and clinical performance, and the underlying educational theory. The focus of the paper is on (1) the credibility of claims (both empirical and theoretical) about the ties between PBL and educational outcomes and (2) the magnitude of the effects. The author reviewed the medical education literature, starting with three reviews published in 1993 and moving on to research published from 1992 through 1998 in the primary sources for research in medical education. For each study the author wrote a summary, which included study design, outcome measures, effect sizes, and any other information relevant to the research conclusion. The review of the literature revealed no convincing evidence that PBL improves knowledge base and clinical performance, at least not of the magnitude that would be expected given the resources required for a PBL curriculum. The results were considered in light of the educational theory that underlies PBL and its basic research. The author concludes that the ties between educational theory and research (both basic and applied) are loose at best.
