This paper examines some of the recent literature on the estimation of production functions. We focus on techniques suggested in two recent papers, Olley and Pakes (1996) and Levinsohn and Petrin (2003). While there are some solid and intuitive identification ideas in these papers, we argue that the techniques can suffer from functional dependence problems. We suggest an alternative approach that is based on the ideas in these papers, but does not suffer from the functional dependence problems and produces consistent estimates under alternative data generating processes for which the original procedures do not.

This paper explores whether one of the most important U.S. policies towards Africa of the past few decades achieved its desired result. In 2000, the United States dropped trade restrictions on a broad list of products through the African Growth and Opportunity Act (AGOA). Since the Act was applied to both countries and products, we estimate the impact with a triple difference-indifferences estimation, controlling for both country and product-level import surges at the time of onset. This approach allows us to better address the "endogeneity of policy" critique of standard difference-indifferences estimation than if either a country or a product-level analysis was performed separately. Despite the fact that the AGOA product list as chosen to not include "import-sensitive" products, and despite the general challenges of transaction costs in African countries, we find that AGOA has a large and robust impact on apparel imports into the U.S., as well as on the agricultural and manufactured products covered by AGOA. These import responses grew over time and were the largest in product categories where the tariffs removed were large. AGOA did not result in a decrease in exports to Europe in these product categories, suggesting that the U.S.-AGOA imports were not merely diverted from elsewhere. We discuss how the effects vary across countries and the implications of these findings for aggregate export volumes.

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