1 weights an article by the journal where it appears based on citations to that journal, using values generated by Laband and Piette (1994). This index distinguishes strongly among journals. For example, the Journal of Political Economy has a weight of 59.1, whereas Economic Inquiry has a weight of 7.9. In constructing I₁ we use the weights associated with the decade in 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]

1 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.

1, 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.

j, j = 1, 2, 3, we estimate b₀ and b₁ in

0 = 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.

j,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.