The purpose of this review is to synthesize all available evaluative r
esearch from 1970 through 1992 that compares problem-based learning (P
BL) with more traditional methods of medical education. Five separate
meta-analyses were performed on 35 studies representing 19 institution
s. For 22 of the studies (representing 14 institutions), both effect-s
ize and supplementary vote-count analyses could be performed; otherwis
e, only supplementary analyses were performed. PBL was found to be sig
nificantly superior with respect to students' program evaluations (i.e
., students' attitudes and opinions about their programs)-dwBAR (stand
ardized differences between means, weighted by sample size) = +.55, CI
.95 = +.40 to +.70-and measures of students' clinical performance (dwB
AR = +.28, CI.95 = +.16 to +.40). PBL and traditional methods did not
differ on miscellaneous tests of factual knowledge (dwBAR = -.09, CI.9
5 = +.06 to -.24) and tests of clinical knowledge (dwBAR = +.08, CI.95
= -.05 to +.21). Traditional students performed significantly better
than their PBL counterparts on the National Board of Medical Examiners
Part I examination-NBME I (dwBAR = -.18, CI.95 = -.10 to -.26). Howev
er, the NBME I data displayed significant overall heterogeneity (Q(t)
= 192.23, p <.001) and significant differences among programs (Q(b) =
59.09, p < .001), which casts doubt on the generality of the findings
across programs. The comparative value of PBL is also supported by dat
a on outcomes that have been studied less frequently, i.e., faculty at
titudes, student mood, class attendance, academic process variables, a
nd measures of humanism. In conclusion, the results generally support
the superiority of the PBL approach over more traditional methods.