t of the economics profession.[7]
Among the several groups of physical scientists analyzed by Levin and Stephan (1992) the decline of productivity (high-quality publishing) with age was very pronounced. McDowell's (1982) small samples of scholars in a variety of disciplines suggest less rapid declines in productivity with age (in publications unweighted by quality), with the sharpest declines and earliest peaks in the "hard" sciences, and later peaks among English professors and historians. The evidence from our two very different types of samples of economists and economics publishing that account for the quality of publications suggests that, for whatever reason, economics is at least as much a "young person's game" as are the physical sciences.
II. Heterogeneity
in Declining Productivity
The evidence in section I documents the decline in productivity at the sample means. Information on the age-productivity relationship at the extremes of the sample is interesting in its own right and might help shed some light on the possible causes of the apparent decline in productivity with age. The simplest test compares productivity losses among the top early performers with that of the entire sample of economists at elite institutions. Among the top 10% of early producers the mean values of I1, I2, and I3 at year 20 were 64, 50, and 22%, respectively. These means are quite close to those listed for the entire sample in table 1. Thus on average early promise seems to be sus无忧论文 【http://www.uklunwen.com】tained in this sample. Of the 12 top researchers on whom we have 20 years of data, five were still among the top dozen producers at year 20.
These conclusions are confirmed when we examine the entire sample. For each index Ij, j = 1, 2, 3, we estimate b0 and b1 in
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Table 3 reports the parameter estimates. For all three indexes productivity in year 20 is positively and significantly related to productivity in year 10. There is also substantial productivity loss. The joint hypothesis that b0 = 1 and b1 = 0 (i.e., no productivity loss) is rejected (F-statistics of 134, 152, and 39, respectively). Productivity loss is least severe in I3, which weights all journals equally, regardless of quality.
If productivity losses were less among economists with high early productivity (high Ij,10), b1 would be negative. In fact, for two of the three indexes the estimated b1 is effectively zero. We cannot reject the hypothesis of a linear relationship between late and early productivity. Only for I3 does it appear that productivity loss is higher for top early producers, and even here the effect is quite small. An economist in the top 10% of this sample at year 10 loses only an additional 0.5 (unweighted) paper compared to an average researcher in this sample at year 10. The very top producers in this elite sample keep on producing high-quality research, but at a slower rate. Those who were not at the top early in t |
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论文题目：
AGING AND PRODUCTIVITY AMONG ECONOMISTS 
