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The proportion having held at least one postdoc was inversely related to the number of years since the Ph.D. was granted, ranging from 27 percent for those more than 25 years since degree award to 40 percent for those with 5 years or less since doctorate.
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By field, the trend toward holding a postdoc was also evident. Doctorates in physics/astronomy showed the largest increase in the proportion who held a postdoc, from 36 percent of the Ph.D.s with more than 25 years since the degree to 72 percent of those 5 years or less since the doctorate. Of biological sciences Ph.D.s with more than 25 years since the doctorate, 45 percent held a postdoc; of those 5 years or less since the doctorate, 71 percent held at least one. Only doctorates in social and health sciences showed a decline in the percentage with at least one postdoc from the cohort more than 25 years since degree to the most recent 5 year cohort.
Reasons for Holding Postdocs
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Of those who had held postdocs at some time in their careers, “additional training in Ph.D. field” was most frequently cited as the primary reason for taking the first postdoc (47 percent), followed by “work with a specific person or place” (21 percent). This distribution was similar for those with only one postdoc and those who held more than one (see Table 26 ).
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By field among those who had ever held a postdoc, additional training was the primary reason cited most frequently (with the exception of doctorates in earth/atmospheric/marine sciences whose primary reason was most often work with a specific person).
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A higher than average proportion of doctorates in engineering and agricultural/ environmental sciences cited employment not available as the reason for their first postdoc (25 and 26 percent, respectively, compared with 11 percent for doctorates overall).
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For those doctorates with multiple postdocs, the primary reasons for the second postdoc were still most likely to be additional training and work with a specific person, but the proportions were closer, 35 and 25 percent, respectively. For those holding multiple postdocs, “other employment not available” was cited as the primary reason for the second postdoc by 14 percent (compared with 9 percent citing this reason for their first postdoc).
