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The self-consistent modeling of vacuum polarization due to virtual electron-positron fluctuations is of relevance for many near term experiments associated with high intensity radiation sources and represents a milestone in describing scenarios of extreme energy density. We present a generalized finite-difference time-domain solver that can incorporate the modifications to Maxwell's equations due to vacuum polarization. Our multidimensional solver reproduced in one-dimensional configurations the results for which an analytic treatment is possible, yielding vacuum harmonic generation and birefringence. The solver has also been tested for two-dimensional scenarios where finite laser beam spot sizes must be taken into account. We employ this solver to explore different types of laser configurations that can be relevant for future planned experiments aiming to detect quantum vacuum dynamics at ultra-high electromagnetic field intensities.

In a randomized control trial, the precision of an average treatment effect estimator can be improved either by collecting data on additional individuals, or by collecting additional covariates that predict the outcome variable. We propose the use of pre-experimental data such as a census, or a household survey, to inform the choice of both the sample size and the covariates to be collected. Our procedure seeks to minimize the resulting average treatment effect estimator's mean squared error, subject to the researcher's budget constraint. We rely on a modification of an orthogonal greedy algorithm that is conceptually simple and easy to implement in the presence of a large number of potential covariates, and does not require any tuning parameters. In two empirical applications, we show that our procedure can lead to substantial gains of up to 58%, measured either in terms of reductions in data collection costs or in terms of improvements in the precision of the treatment effect estimator., Comment: 54 pages, 1 figure

When describing the determinants of economic or social outcomes, economists often have a very simplified view of skill. Failure to take into account the fact that skill is intrinsically a multidimensional object may misguide both research and the design of social policy. In this paper, the authors analyse the consequences and determinants of cognitive and noncognitive (social) skills at age 11, using data for Great Britain from the National Child Development Survey (NCDS). The authors document the importance of these skills for schooling attainment, labour market outcomes and social behaviours at various ages, and analyse the role of family background and the home learning environment in the formation of these skills. The authors find that an overall measure of non-cognitive skill is important for a host of outcomes, including whether or not an individual stays on at school beyond the age of 16, whether they have obtained a degree by age 42, employment status at age 42, work experience between ages 23 and 42, wages at age 42, smoking at age 16, truancy before age 16, exclusion from school, teenage pregnancy, involvement with crime (ages 16 and 42), and health at age 42. Furthermore, the impact of this measure of non-cognitive skill does not differ in any systematic way across particular subgroups of interest (including those defined according to parental education, or father's socioeconomic status). The authors go on to split this measure of non-cognitive skill into twelve different domains. As an example, the authors find that "inconsequential behaviour" at age 11 (for example, misbehaviour in class) is associated with a reduction in the probability that an individual will stay on at school beyond age 16, a reduction in their wages at age 42, an increase in the likelihood that they will be a heavy smoker at age 16, and an increase in the probability that they will have played truant or been involved in crime by age 16. Further, the authors find that depression at age 11 is associated with a reduction in the probability that an individual will have obtained a degree by age 42, an increase in the probability that the individual will be a heavy smoker at age 16, an increase in the likelihood that they will have been excluded from school, and an increase in the probability that they will report symptoms of depression at age 42. These findings together make it clear that a vision of the world in which skill is thought of as a one-dimensional object is extremely inadequate. Further, the authors show that both cognitive and non-cognitive skills are strongly dependent on family background and other characteristics of the home learning environment, and that this is likely to be for both genetic and environmental reasons. More importantly, their work suggests that social skills may be more malleable than cognitive skills, which--if true--suggests that there may be greater scope for education policy to affect social skills rather than cognitive skills. Appended are: (1) Data; (2) Impact of family background controls; and (3) Differences between subgroups of interest. (Contains 22 tables, 8 figures and 72 footnotes.)

This paper summarizes research on evaluating the distributional consequences of social programs, presenting the evaluation problem for an economy with two sectors (e.g., schooled and unschooled) where agents select or are selected into treatment (one of the two sectors). It considers policies affecting choices of treatment but not potential outcomes (the outcomes they experience under different treatments) and compares outcomes across two policy regimes that affect treatment choices. This task is easier when individuals respond in the same way to treatment than when they differ in their response and act on those differences in making treatment choice decisions. In the latter case, the marginal entrant into schooling is not the same as the average participant in treatment, and the representative agent paradigm breaks down. The paper estimates the distributional consequences of two proposed policy reforms in U.S. education. Even though they barely affect the overall distribution of outcomes, and would be judged equivalent to the pre-policy origin state under the Veil of Ignorance criterion, they have substantial effects on a small group of people concentrated in the middle to high end of the pre-policy wage distribution. An appendix shows how to generate the counterfactual distributions of outcomes produced by alternative policies. (Contains 23 references.)(SM)