ریسک سرمایه انسانی در اقتصاد چرخه عمر

The aggregate effects of market incompleteness are studied in a model where agents face idiosyncratic, uninsurable human capital investment risk. Using a life-cycle model with a version of a Ben-Porath (1967) human capital accumulation technology, stationary equilibria of calibrated cases are analyzed in which risk arises from specialization risk and career risk. With career risk only, stationary equilibria resemble those studied by Aiyagari (1994), and the impact of uninsurable idiosyncratic risk is relatively small. With a significant amount of specialization risk, however, stationary equilibria are severely distorted, with human capital about 57 percent as large as its complete markets counterpart.

Dispersion of labor earnings increases over the life-cycle, a well documented feature of the U.S. data. According to Deaton and Paxson (1994), within-cohort labor income inequality increases with age. In related work, Huggett et al. (2009) investigate the reasons behind this rise in earnings dispersion and find that about one-third of the variation in lifetime earnings is due to idiosyncratic human capital shocks. Other cross sectional studies also indicate that agents face a great deal of uncertainty when making their schooling decisions.1 Taken together, it appears that investment in human capital is risky and part of the labor income uncertainty that agents face over their life-cycle is a manifestation of this idiosyncratic human capital risk. In addition, it is widely understood that human capital investment is uninsurable. One main consequence of this type of labor income uncertainty is that it could deter investment in human capital. If a mechanism like this is at work in actual economies, the impact of market incompleteness on the aggregate economy could be large,2 possibly calling for policy intervention to mitigate the effect of this risk on household decisions to invest in training. This paper studies the macroeconomic implications of labor income uncertainty arising from the risky nature of human capital investment. It uses a specification that allows a direct analysis of the impact of risk on the accumulation of human capital, helps isolate and quantify the effect of risk on individual decisions, and allows commentary on the divergent views in the literature on the role of market incompleteness in the aggregate economy.

The impact of uninsurable idiosyncratic human capital risk in a general equilibrium life-cycle model is studied in this paper. The results indicate that the nature of risk, career versus specialization, is crucial in determining the quantitative implications of market incompleteness for the aggregate economy. Calibrated stationary equilibrium with only career risk has properties similar to Aiyagari (1994) reconfirming the long held belief that the quantitative implications of uninsurable idiosyncratic risk are inconsequential. However, the baseline calibration with high weight on the specialization risk illustrates that market incompleteness can have large, quantitatively significant, macroeconomic implications. Stationary equilibrium in this case is severely distorted relative to the complete markets benchmark. The quantitative analysis also suggests that in order to comment on the aggregate effect of uninsurable idiosyncratic human capital risk, empirical studies based on micro data would need to determine the nature of human capital risk. Such studies could thereby alert us about the likely extent of distortion due to uninsurable idiosyncratic human capital risk.