英语论文网

rent 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 sustained 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 Multiple line equation(s) cannot be represented in ASCII text. (1) 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 their careers slow down as rapidly as the top people, but their slowdown leads them to publish increasingly in lower quality outlets. Another way of examining heterogeneity is to look at how authors of different quality free in the publication process conditional on their efforts. We obtained data on a random sample of initial submissions to a major general journal during a four-month period in 1991. (Some of the data were initially supplied by the journal's office for use in Hamermesh (1994).) Refereeing at this journal is double-blind, so that the chance that referees (though possibly not the editors) were affected by authors' reputations is reduced. The ages of the authors of these 313 papers are measured as of 1993 to account for the probable two-year average lag between the submission of a paper and its publication. The simple fact in these additional data is that acceptance rates at this journal are remarkably constant by author's age. The probabilities of an article being accepted are 0.122, 0.114, and 0.123 in the three age groups 50, respectively.[8] On average there is no decline with age in the acceptance rate of papers submitted to this journal.[9] Probits on the acceptance of a submission that also included variables indicating whether the author was a member of the AEA, was in a top 20 department (as listed in Blank, 1991), was resident in North America, or was female, and the author's prior citation record yield an identical conclusion. The declining presence of older authors in top economics journals does