[Excerpt] On average, the typical American citizen who received a PhD during the last 40 years did so approximately 9 years after she received her bachelor’s degree. Thus, if we divide the number of American citizens receiving PhDs in a year by the number of American citizens receiving bachelor’s degrees 9 years earlier, we obtain an estimate of the fraction of American citizen college graduates in the earlier year who ultimately receive PhDs. This fraction rose from .042 for 1954 bachelor’s recipients (1963 PhDs) to about .07 for 1962 bachelor’s recipients (1971 PhDs). The fraction then plummeted over the next decade falling to .026 for 1973 bachelor’s recipients (1982 PhDs) and has been relatively stable, fluctuating between .025 and .028, since then. Of course changes in the probability that bachelor’s recipients go on to receive PhDs nationwide are influenced by many changing demographic trends including changes in high school graduation rates, changes in college enrollment rates of high school graduates, changes in college graduation rates for college enrollees, changes in the distribution of undergraduate majors, and changes in the academic backgrounds of college students. In this paper we focus on a more homogenous set of 31 highly selective private colleges and universities. The academic aptitudes and preparations of students attending these institutions are among the highest in the nation and make this group’s students’ behavior of special interest.