THE EVOLUTION OF THE SCIENTIFIC PRODUCTIVITY OF HIGHLY PRODUCTIVE ECONOMISTS

This paper studies the evolution of research productivity of a sample of economists working in the best 81 departments in the world in 2007. The main novelty is that, in so far as a productivity distribution can be identified with an income distribution, we measure productivity mobility in a dynamic context using an indicator inspired in an income mobility index suggested by Fields (2010) for a two‐period world. Productivity is measured in terms of publications, weighted by the citation impact of the journals where each article is published in the periodical literature. We study the evolution of average productivity, productivity inequality, the extent of rank reversals, and productivity mobility for seven cohorts, as well as the population as a whole. We offer new evidence confirming previous results about the heterogeneity of the evolution of productivity for top and other researchers. However, the major result is that—contrary to what was expected—for our sample of very highly productive scholars the effect of rank reversals between the two periods on overall productivity mobility offsets the effect of an increase in productivity inequality from the first to the second period in the youngest five out of seven cohorts. (JEL A11, A12, B41, D63, I32)     

A Kernel Variogram Estimator for Clustered Data

Abstract.  The variogram provides an important method for measuring the dependence of attribute values between spatial locations. Suppose that the nature of the sampling process leads to the presence of clustered data; it would be advisable to use a variogram estimator that aims to adjust for clustering of samples. In this setting, the use of a non-parametric weighted estimator, obtained by considering an inverse weight to a given neighbourhood density combined with the kernel method, seems to have a satisfactory behaviour in practice. This paper pursues a theoretical study of the cluster robust estimator, by proving that it is asymptotically unbiased as well as consistent and by providing criteria for selection of the bandwidth parameter and the neighbourhood radius. Numerical studies are also included to illustrate the performance of the considered estimator and the suggested approaches.