perhaps reflecting the fact that dentists are included in this group), followed by M.D.-Ph.D.s (21.3 percent). As a group, Ph.D.s were least likely to conduct clinical research: only 18 percent did so.

Previous NRC analyses of clinical research have generally assumed that Ph.D.s conducting clinical research were trained in the health science disciplines listed in Appendix E , including fields such as environmental health, epidemiology, health services, nursing, and pharmacy. Yet the data on federally funded clinical research collected over the last few years reveal a workforce that is much more complex than previously recognized. According to this new information, the pool of investigators conducting clinical research supported by the NIH and AHRQ includes many who were trained in the behavioral and social sciences and, to a lesser extent, the basic biomedical sciences.

Among those whose fields of study could be identified, more Ph.D.s conducting clinical research received their degrees in clinical psychology (13.4 percent) than in any other discipline. Other fields producing large numbers of clinical investigators (listed in Table 4-2 ) included such traditional disciplines as epidemiology and nursing, as well as those less commonly associated with clinical research, including sociology, biochemistry, and physiology.

By adopting a definition of clinical research that encompasses behavioral and social science studies, the