I. INTRODUCTION over the past ten years, the debate over welfare reform has been transformed by Jeffrey Grogger and his coauthors. Grogger's data-driven research shows, among other things, that work requirements and time limits may have no effect on marriage or fertility rates. (1) In other words, welfare does not produce "welfare queens." More recently, Roland Fryer and Steven Levitt have discredited Herrnstein's theory that the test score gap between Caucasians and African Americans is the result of biological differences. Fryer and Levitt used longitudinal data to document for the first time that there are no differences in the cognitive skills of white and black nine-month-old babies, and that the gap that develops by elementary school is explained almost entirely by socio-economic and environmental factors. (2) And in 2001, John J. Donohue and Steven D. Levitt presented shocking evidence that the decline in crime rates during the 1990s, which had defied explanation for many years, was caused in large measure by the introduction of legalized abortion a generation earlier. (3)
