One of the areas of policy research where randomized field trials have been utilized most intensively is welfare reform. Starting in the late 1960s with experimental tests of a negative income tax and continuing through current experimental tests of recent welfare reforms, randomized evaluations...

We consider the sensitivity of the Tobit estimator to heteroscedasticity. Our single independent variable is a dummy variable whose coefficient is a difference between group means, and the error variance differs between groups. Heteroscedasticity biases the Tobit estimate of the two means in...

The aim of this note is to interpret estimation of the conventional treatment-effect selection-bias model in econometrics as a method of aggregation and to draw the implications of this interpretation. In addition, the paper notes the connection of this interpretation with an older style of...

In this paper, we propose a parametric spectral estimation procedure for constructing heteroskedasticity and autocorrelation consistent (HAC) covariance matrices. We establish the consistency of this procedure under very general conditions similar to those considered in previous research, and we...

This paper presents a new numerical method for solving general equilibrium models with many assets. The method can be applied to models where there are heterogeneous agents, time-varying investment opportunity sets, and incomplete markets. It also can be used to study models where the...

It has recently been observed that when equations of motion for state variables are nonautonomous, optimal control problems involving Uzawa's endogenous rate of time preference cannot be solved using the change-of-variables method common in the literature. Instead, the problem must be solved by...

We analyze how uncertainty about when information about future returns to a project may be revealed affects investment. While 'good news' about future returns boosts investment, 'good news about news' (that is news that information may arrive sooner) is shown to depress investment. We show that...

Recent work by Said and Dickey (1984 ,1985) , Phillips (1987), and Phillips and Perron(1988) examines tests for unit roots in the autoregressive part of mixed autoregressive-integrated-moving average (ARIHA) models (tests for stationarity). Monte Carlo experiments show that these unit root tests...

This article compares two leading models of asset pricing: the capital asset pricing model (CAPM) and the arbitrage pricing theory (APT): I argue that while the APT is compatible with the data available for testing theories of asset pricing, the CAPM is not. In reaching this conclusion emphasis...

This paper discusses the estimation of serial correlation in fixed effects models for longitudinal data. Like time series data, longitudinal data often contain serially correlated error terms, but the autocorrelation estimators commonly used for time series, which are consistent as the length of...