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This paper exploits a new source of variation in Head Start funding to identify the program’s effects on health and schooling. In 1965 the Office of Economic Opportunity (OEO) provided technical assistance to the 300 poorest counties to develop Head Start proposals. The result was a large and lasting discontinuity in Head Start funding rates at the OEO cutoff for grant-writing assistance. We find evidence of a large drop at the OEO cutoff in mortality rates for children from causes that could be affected by Head Start, as well as suggestive evidence for a positive effect on educational attainment.

This paper surveys the field of asset pricing. The emphasis is on the interplay between theory and empirical work and on the trade-off between risk and return. Modern research seeks to understand the behavior of the stochastic discount factor ~SDF! that prices all assets in the economy. The behavior of the term structure of real interest rates restricts the conditional mean of the SDF, whereas patterns of risk premia restrict its conditional volatility and factor structure. Stylized facts about interest rates, aggregate stock prices, and cross-sectional patterns in stock returns have stimulated new research on optimal portfolio choice, intertemporal equilibrium models, and behavioral finance. This paper surveys the field of asset pricing. The emphasis is on the interplay between theory and empirical work. Theorists develop models with testable predictions; empirical researchers document “puzzles”—stylized facts that fail to fit established theories—and this stimulates the development of new theories. Such a process is part of the normal development of any science. Asset pricing, like the rest of economics, faces the special challenge that data are generated naturally rather than experimentally, and so researchers cannot control the quantity of data or the random shocks that affect the data. A particularly interesting characteristic of the asset pricing field is that these random shocks are also the subject matter of the theory. As Campbell, Lo, and MacKinlay ~1997, Chap. 1, p. 3! put it: What distinguishes financial economics is the central role that uncertainty plays in both financial theory and its empirical implementation. The starting point for every financial model is the uncertainty facing investors, and the substance of every financial model involves the impact of uncertainty on the behavior of investors and, ultimately, on mar-* Department of Economics, Harvard University, Cambridge, Massachusetts

This reprinting is corrected to software version 2.10

Effects of preoperative feeding with a whey protein plus carbohydrate drink on the acute phase response and insulin resistance. A randomized trial

and significantly different from zero even when time aggregation is taken into account. We thank Robert Barsky, Miles Kimball, Matthew Shapiro, seminar participants

The Balassa-Samuelson model, which explains real exchange rate movements in terms of sectoral productivities, rests on two components. First, it implies that the relative price of non-traded goods in each country should reflect the relative productivity of labor in the traded and non-traded goods sectors. Second, it assumes purchasing power parity holds for traded goods. We test both of these using a panel of OECD countries. Our results suggest that relative prices generally reflect relative labor productivities in the long run. The evidence on purchasing power parity in traded goods is less favorable, at least when we

Abstract: The challenge of effective merger enforcement is tremendous. U.S. antitrust agencies must, by statute, quickly forecast the competitive effects of mergers that occur in virtually every sector of the economy to determine if mergers can proceed. Surprisingly, given the complexity of the regulators task, there is remarkably little empirical evidence on the effects of mergers to guide regulators. This paper describes the necessity of retrospective analysis of past mergers in building an empirical basis for antitrust enforcement, and provides guidance on the key measurement issues researchers confront in estimating the price effects of mergers. We also describe how evidence from merger retrospectives can be used to evaluate the economic models used to predict the competitive effects of mergers. The views expressed in this paper are those of the authors and not necessarily represent those of the U.S. Federal Trade Commission or any individual Commissioner. We would like to thank The Federal Trade Commission and the Department of Justice attempt to block or modify only those mergers that would reduce consumer welfare. The challenge of effective enforcement is enormous. The antitrust agencies have relatively little time to