(June 2014) Regional economists use the shift-share analysis method to determine how much of regional job growth can be attributed to national trends and how much is due to unique regional factors. We adapted this method to examine growth in biomedical postdoctoral employment in U.S. research education institutions.

We looked at employment growth in three time periods corresponding to shifts in the National Institutes of Health funding levels. From October 1998 to September 2003, the NIH budget doubled, growing at about 15 percent annually. From 2003 to 2009, growth in the NIH annual budget slowed to between 1 percent and 3 percent per year, growing by about 8 percent. National growth in biomedical postdoctoral employment rose from 14.6 percent to 19.6 percent, then fell back to 15.2 percent in the respective periods.

To conduct shift-share analysis, we split biomedical postdoctoral employment job growth into three components: subfield mix effect, national postdoctoral employment growth effect, and demographic subgroup competitive advantage. For the purposes of this analysis, we focus primarily on each demographic subgroup’s competitive advantage.

Shift-Share Components

  • The Subfield Mix Effect represents the demographic subgroup’s share of biomedical postdoctoral employment growth that is explained by biomedical postdoctoral employment growth of the specific subfield at the national level.
  • The National Growth Effect explains how much of the demographic subgroup’s growth in biomedical postdoctoral employment may be explained by the overall growth of national biomedical postdoctoral employment: If employment of biomedical postdoctoral trainees in the nation as a whole is growing, one would generally expect to see some positive change in each subfield for each demographic subgroup.
  • The Demographic Subgroup’s Competitive Advantage in a subfield indicates how much of the change in a given subfield is due to some unique (unmeasured) advantage that the subgroup possesses because the growth in biomedical postdoctoral employment cannot be explained by expected change. Here expected change is the sum of the subfield mix effect and the national growth effect. A positive competitive effect for a demographic subgroup in a subfield indicates the subgroup is outperforming national trends (both overall national trends and national trends in that specific industry). A negative effect means that subgroup in a subfield is underperforming compared to national trends.

By definition, the sum of the shift-share components for any demographic subgroup must equal the total change in biomedical postdoctoral employment for that same subgroup over all subfields in the time period. Also, the sum of all demographic subgroups’ competitive advantages across the subfields must equal zero.

Competitive Advantage

No clear story emerges about how competitive advantage in postdoctoral biomedical employment differs by citizenship/visa status. Both male and female “foreign-born” (temporary visa holders) experienced better-than-expected growth in biomedical postdoctoral employment during the rapid growth in funding from 1998 to 2003.