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Most papers that employ Differences-in-Differences estimation (DD) use many years of data and focus on serially correlated outcomes but ignore that the resulting standard errors are inconsistent. To illustrate the severity of this issue, we randomly generate placebo laws in state-level data on female wages from the Current Population Survey. For each law,(More)
Two recent papers, Deaton (2009), and Heckman and Urzua (2009), argue against what they see as an excessive and inappropriate use of experimental and quasi-experimental methods in empirical work in economics in the last decade. They specifically question the increased use of instrumental variables and natural experiments in labor economics, and of(More)
Most papers that employ Differences-in-Differences estimation (DD) use many years of data and focus on serially correlated outcomes but ignore that the resulting standard errors are inconsistent. To illustrate the severity of this issue, we randomly generate placebo laws in state-level data on female wages from the Current Population Survey. For each law,(More)
First version: 16 July 1996 This version: 1 March 2001 I argue for thinking of program evaluation as a decision problem. There are two steps. First, a counselor determines which program (treatment or control) each individual joins, based for example on maximizing the probability of employment or expected earnings. Second, the policymaker decides whether: to(More)
Temporary employment contracts allowing unrestricted dismissals were introduced in Spain in 1984 and quickly came to account for most new jobs. In 1997, however, the Spanish government attempted to reduce the incidence of temporary employment by reducing payroll taxes and dismissal costs for permanent contracts. In this paper, we exploit the fact that(More)
This paper shows that moment inequality tests that are asymptotically similar on the boundary of the null hypothesis exist, but have poor power. Hence, existing tests in the literature, which are asymptotically non-similar on the boundary, are not de…cient. The results are obtained by …rst establishing results for the …nite-sample multivariate normal(More)
Four rankings of economics departments worldwide in terms of graduate education are constructed. The central methodological idea is that the value of a department is the sum of the values of its PhD graduates, as reflected in the values of their current employing departments. Scores are derived as solutions to linear simultaneous equations in the values.(More)
We measure the causal effects of online advertising on sales, using a randomized experiment performed in cooperation between Yahoo! and a major retailer. After identifying over one million customers matched in the databases of the retailer and Yahoo!, we randomly assign them to treatment and control groups. We analyze individual-level data on ad exposure(More)
We estimate a structural equilibrium model of the automatic teller machine market (ATM) to evaluate the implications of regulating ATM surcharges. We use data on bank characteristics, potential and actual ATM locations, and consumer locations; identify the model parameters with a regression discontinuity design; and develop methods to estimate the model(More)