The relationship between age and the publishing productivity of Ph.D. scientists is analyzed using data from the Survey of Doctorate Recipients (National Research Council) and the Science Citation Index. The longitudinal nature of the data allows for the identification of pure aging effects. In five of the six areas studied, life-cycle aging effects are present. Only in particle physics, where scientists often speak of being on a "religious quest," is there indication that scientific productivity is not investment-motivated. Vintage effects are also considered. The expectation that the latest educated are the most productive is not generally supported by the data.

The relationship between age and the publishing productivity of Ph.D. scientists is analyzed using data from the Survey of Doctorate Recipients (National Research Council) and the Science Citation Index. The longitudinal nature of the data allows for the identification of pure aging effects. In five of the six areas studied, life-cycle aging effects are present. Only in particle physics, where scientists often speak of being on a "religious quest, " is the indication that scientific productivity is not investment-motivated. Vintage effects are also considered. The expectation that the latest educated are the most productive is not generally supported by the data. Copyright 1991 by American Economic Association.

U.S. research universities are increasingly populated by postdoctoral fellows. Two dimensions of the postdoctoral training have led to this increase. One is the increasing number of new Ph.D. s taking a first postdoc position, and the other involves a lengthening of the duration of an individual’s postdoc experience. In this paper, we examine factors contributing to both of these trends. We find that the increased propensity to take a postdoctoral position can be attributed to the increased proportion of Ph.D.s being awarded in the life sciences and the increased proportion of temporary and permanent residents in the graduate population. The increased propensity to take a postdoc position also relates to adverse job market conditions experienced by Ph.D. s during the period. Our postdoc duration results suggest that increased duration can be explained in part by the increasing proportion of Ph.D. s awarded to temporary residents and the increased number of degrees being awarded in the life sciences. Adverse job market conditions also appear to play a role. We also find the duration of the postdoc experience to be positively related to the provision of fringe benefits. We would like to thank Grant Black of the Andrew Young School for his assistance. We also thank Science Resources Statistics, National Science Foundation for providing U.S. access to the Survey of Doctorate Recipients and the Survey of Earned Doctorates. We have benefited from the comments of Robert Clark, Richard Freeman, Bill Amis, Michael Rothchild and participants at the November 2004 NBER Education meeting. Stephan would like to acknowledge the financial support provided by the TIAA-CREF Institute for this project and from the Andrew W. Mellon Foundation for support of work with the Survey of Earned Doctorates.