AGING AND PRODUCTIVITY AMONG ECONOMISTS (来源：EnglishCN.com)

Abstract--Economists' productivity over their careers and as measured by publication in leading journals declines very sharply with age. There is no difference by age in the probability that an article submitted to a leading journal will be accepted. Rates of declining productivity are no greater among the very top publishers than among others, and the probability of acceptance is increasingly related to the author's quality rather than the author's age.

It is well known that productivity declines with age in a wide range of activities. Lehman (1953) suggests an early peak in productivity in a variety of scientific and artistic endeavors, and Diamond (1986) documents the pattern for several scholarly pursuits. Levin and Stephan (1992) provide clear evidence that this decline exists even after careful attempts to account for individual and cohort differences. Fair (1994) finds declines in physical ability among elite runners, as does Lydall (1968,pp. 113 passim) in physical abilities of the population generally. In this study we examine productivity declines in our own field. The main new results arise from our use of two different types of information, the equivalent of household and establishment data, to study the stone field over essentially the same period of time. Section I discusses the general results on aging and productivity, whereas section II presents evidence of the importance of heterogeneity.

which the articles were published. I₂ distinguishes somewhat less among journals by assigning all articles in the nine "core" journals identified by Laband and Piette a value of 1, whereas all other journals are valued at 0.5.[3] Finally, I₃ gives all papers a weight of 1. Coauthored articles were given half credit, consistent with Sauer's (1988) findings on the economic returns to coauthorship.[4]

We measure the change in productivity over the life cycle by the percentage change in the number of publications from 9-10 years past the Ph.D. to the periods 14-15 years and then 19-20 years after. For most of the elite economists the base period is equivalent (accounting for publication lags) to the time of tenure, when one might expect that incentives to produce are at a peak. Using two-year publication records at each point reduces the effects of noise in the performance measures. One might argue that still other scientific life-cycle mileposts (e.g., attaining a full professorship) should be accounted for too (and to some extent the 14-15-year point does this). But our main purpose is simply to provide detailed evidence on the relationship to age, and our data are not sufficient to infer the impact of every possible milepost.

Table 1 contains data on productivity loss by Ph.D. vintage measured by each of the three indexes. If we consider I₁ and I₂, the two indexes that take journal quality into account, the decline appears to be quite substantial. Between years 9-10 and 14-15 elite economists as a group lose 29 to 32% of their output. From years 9-10 to 19-20 they lose 54 to 60%. In other words, productivity losses are on the order of 5 % per year from the time of peak productivity. However, the losses do not appear to accelerate over these 10 years of the economists' work lives. The loss from year 10 to year 20 is approximately twice that from year 10 to year 15.