The Marginal Product of Capital
利用宏观数据发现各国资本边际产出惊人相似，反驳了国际信贷摩擦阻碍资本流向穷国的观点，并指出穷国资本比率低源于互补要素不足和效率低下。
Whether or not the marginal product of capital (MPK) differs across countries is a question that keeps coming up in discussions of comparative economic devel-opment and patterns of capital flows. Using easily accessible macroeconomic data we find that MPKs are remarkably similar across countries. Hence, there is no prima facie support for the view that international credit frictions play a major role in preventing capital flows from rich to poor countries. Lower capital ratios in these countries are instead attributable to lower endowments of complementary factors and lower efficiency, as well as to lower prices of output goods relative to capital. We also show that properly accounting for the share of income accruing to reproducible capital is critical to reach these conclusions. One implication of our findings is that increased aid flows to developing countries will not significantly increase these countries ’ capital stocks and incomes. I.