Problem-based learning: why curricula are likely to show little effect on knowledge and clinical skills

OBJECTIVES: A recent review of problem-based learning's effect on knowledge and clinical skills updated findings reported in 1993. The author argues that effect sizes (ES) seen with PBL have not lived up to expectations (0.8-1.0) and the theoretical basis for PBL, contextual learning theory, is weak. The purposes of this study were to analyse what constitutes reasonable ES in terms of the impacts on individuals and published reports, and to elaborate upon various theories pertaining to PBL. DESIGN: Normal theory is used to demonstrate what various ESs would mean for individual change and a large meta-analysis of over 10 000 studies is referred to in identifying typical ESs. Additional theories bearing upon PBL are presented. RESULTS: Effect sizes of 0.8-1.0 would require some students to move from the bottom quartile to the top half of the class or more. The average ES reported in the literature was 0.50 and many commonly used and accepted medical procedures and therapies are based upon studies with ESs below 0.50. CONCLUSIONS: Effect sizes of 0.8-1.0 are an unreasonable expectation from PBL because, firstly, the degree of changes that would be required of individuals would be excessive, secondly, leading up to medical school, students are groomed and selected for success in a traditional curriculum, expecting them to do better in a PBL curriculum than a traditional curriculum is an unreasonable expectation, and, thirdly, the average study reported in the literature and many commonly used and accepted medical procedures and therapies are based upon studies having lesser ESs. Information-processing theory, Cooperative learning, Self-determination theory and Control theory are suggested as providing better theoretical support for PBL than Contextual learning theory. Even if knowledge acquisition and clinical skills are not improved by PBL, the enhanced work environment for students and faculty that has been consistently found with PBL is a worthwhile goal.