Comparison of growth rates of PBL and biomedical knowledge. (A), Relative growth of interest in PBL versus lecture-based teaching based on PubMed keyword frequencies between 1975 and 2000. The Title fields of the journal database were searched each year for the strings "problem-based learning" (open squares) or "lecture" (open diamonds); the retrieved items were then scrutinized to determine those dealing with the subject of teaching style (e.g., eponymous "lectures" were excluded). (B), Growth rates of journal articles dealing with subject matter relating to science, medicine and education. The strings "gene" (solid diamonds), "clinical" (open squares) and "medical education" (solid triangles) are shown here, illustrative of the frequencies of many other keywords searched.