[12] Although the formal job title is often postdoctoral fellowship or research associate, many different titles are used. This chapter will generally use the shorter, more commonly used, and best understood name, "postdoc." A postdoc has traditionally been defined as a temporary position, after completion of a doctorate, taken primarily for additional training—a period of advanced professional apprenticeship.

[13] Some part of the citizen and permanent resident postdoc population in the fall of 2005 will not be counted even in SDR. Excluded are summer 2005 graduates who may be in postdoc positions in the fall of 2005, doctorate holders who may have left the country before April 2006, and those who have foreign doctorates.

[14] A 2003 survey conducted by the Sigma Xi honor society, which was nonrepresentative and likely to undercount foreign postdocs, found that 46% of responding postdocs had received their doctorate from a non-U.S. institution.

[15] Respondents also had to be under age 76 and resident in the United States in April 2006. In a similar retrospective question on the 1995 SDR, 25% of those earning their doctorates before 1964 reported having had postdocs.