FIGURE D-1 U.S.-trained Ph.D. workforce, in thousands, in three major fields, 1973-2006: quadratic trend and annual variations.

SOURCE: Data extracted from National Science Foundation Survey of Doctorate Recipients, 1973-2006 and NRC analysis.

These estimates of the workforce cover not only those employed in jobs related to science (which includes those on postdoctorates) but also those in nonscience jobs, as well as the unemployed and those not looking for work—often women taking a break from employment (Figure D-2). The estimates exclude the retired. In 2006, those actually employed in science were 80-83 percent of the total workforce. This is a lower proportion than the historical average up to 2001, which is around 90 percent in each field. What has taken the place of jobs in science is non-science employment. In the Ph.D. surveys from 1973 to 2001, the proportion of the workforce employed in non-science jobs did not exceed 10 percent in any field, except once, just barely, among behavioral scientists in 1995. In the two surveys since 2001, in contrast, this proportion has been between 13 and 18 percent in each field.

Postdoctorates have been an important category of science employment, particularly for younger scientists. Across all fields, those on postdoctorates were 17,000 in 2006, or 7.8 percent of all those in science employment. For scientists under 35, postdoctorates made up 42 percent of science employment. The 2006 figures represented increases from 2001 and particularly 2003, when absolute numbers on postdoctorates actually declined. Although 17,000 was the highest figure recorded in the biennial surveys, in percentage terms it represented no more than a return to the levels of the late 1990s.

Another change in the U.S.-trained workforce, but one that has been largely gradual, is the increasing proportion of women (Figure D-3). Shortly after 2003, behavioral scientists reached a turning point, with the sex ratio falling to 100, or equal numbers of men and women. Among clinical scientists, this turning point was reached in 1994, and the sex ratio was down by 2006 to 64 men per 100 women and still falling. Among biomedical scientists, the sex ratio was still elevated at 175 in 2006, although extrapolation of current trends suggests that equality could be reached around 2020.