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Advanced human capital requires "basic" human capital as an input. Physical capital does not, in general, have such hierarchical structure. This paper models optimal investment in hierarchical human capital as well as nonhierarchical physical capital. The authors analyze the steady state, transition dynamics, and endogenous growth properties of the system. The optimal program exhibits non-monotonicities in human capital stocks. This result has important implications for the optimal timing of investment in hierarchical human capital. The analysis also addresses the debate regarding the distribution of education expenditures and the divergence between ex-post and ex-ante rates of return to education.

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This article investigates monopoly and oligopoly provision of an addictive good. Consumer preferences are modeled as in Becker and Murphy (1988). Addictive goods have characteristics that create interesting strategic issues when suppliers are noncompetitive. We characterize the perfect Markov equilibrium of a market with noncompetitive supply of an addictive good and compare it with the efficient solution. Depending on particular parameter values, we find a wide variety of possible steady-state outcomes, including ones with output above the efficient level and price below marginal cost. We also find that market power can be disadvantageous.

We investigate how increases in publication delays have affected the life cycle of publications of recent Ph.D. graduates in economics. We construct a panel dataset of 14,271 individuals who were awarded Ph.D.s between 1986 and 2000 in U.S. and Canadian economics departments. For this population of scholars, we amass complete records of publications in peer-reviewed journals listed in the JEL (a total of 368,672 observations). We find evidence of significantly diminished productivity in recent relative to earlier cohorts when productivity of an individual is measured by the number of AER-equivalent publications. Diminished productivity is less evident when the number of AER-equivalent pages is used instead. Our findings are consistent with earlier empirical findings of increasing editorial delays, decreasing acceptance rates at journals, and a trend toward longer manuscripts. This decline in productivity is evident in both graduates of top 30 and non-top 30 ranked economics departments and may have important implications for what should constitute a tenurable record. We also find that the research rankings of top economics departments are a surprisingly poor predictor of the subsequent research rankings of their Ph.D.s graduates. (JEL A11, J24, J29, J44)