D-Branes and Spin^c Structures

It was recently pointed out by E. Witten that for a D-brane to consistently wrap a submanifold of some manifold, the normal bundle must admit a Spin^c structure. We examine this constraint in the case of type II string compactifications with vanishing cosmological constant, and argue that in all such cases, the normal bundle to a supersymmetric cycle is automatically Spin^c.Comment: 9 pages, LaTe

Welfare Reform and Non-Marital Fertility in the 1990s: Evidence from Birth Records

The 1996 Personal Responsibility Work Opportunity Reconciliation Act dramatically altered the economic incentive to bear children out-of-wedlock for economically disadvantaged women or couples most likely to avail themselves of welfare programs. We use data from vital statistics and a difference-in-differences research design to investigate whether state and federal welfare reform in the 1990s reduced rates of non-marital childbearing among women aged 19 to 39 at highest risk of welfare use, relative to women at lower risk. We find little consistent evidence for an effect of welfare reform on non-marital childbearing. This finding is similar to the literature that found little or mixed evidence for an effect of AFDC benefits. If anything, federal welfare reform has been associated with a small positive effect of two to three percent for white and black women ages 19 to 39.

Effect of Insurance on Infant Health: A Case Study of Low-Income Women in New Jersey

There have been relatively few evaluations of the effect of private insurance and Medicaid on infant health, and results from previous studies are inconclusive. The objective of this study if to estimate the effect of private insurance coverage and Medicaid participation on birth weight and the incidence of low-birth weight controlling for non-random selection of insurance status. Our data consist of vital records that have been linked to hospital discharge records and Medicaid claims for all births to women in New Jersey in the years 1989 and 1990. We use ordinary least squares regression and instrumental variables procedures to obtain estimates of the effect of insurance status on birth weight. We limit our analysis to low-income women as this is the population most at risk of an adverse birth outcome and the target of Medicaid. The results indicate that Medicaid has a small effect on the incidence of low-birth weight for black women, but has little effect on average birth weight for low-income women. Our preferred estimates suggest that Medicaid participation reduces the incidence of low-birth weight for black women by between 5 and 10 percent. A similar finding was found with regard to private insurance. Private insurance had little effect on average birth weight for both black and white women, and reduced the incidence of low-birth weight for black and white women by between 15 and 25 percent.Insurance, Medicaid, Infants

Explaining the socio-economic gradient in child outcomes: the intergenerational transmission of cognitive skills

Papers in this volume and elsewhere consistently find a strong relationship between children's cognitive abilities and their parents' socio-economic position (SEP). Most studies seeking to explain the paths through which SEP affects cognitive skills suffer from a potentially serious omitted variables problem, as they are unable to account for an important determinant of children's cognitive abilities, namely parental cognitive ability. A range of econometric strategies have been employed to overcome this issue, but in this paper, we adopt the very simple (but rarely available) route of using data that includes a range of typically unobserved characteristics, such as parental cognitive ability and social skills. In line with previous work on the intergenerational transmission of cognitive skills, we find that parental cognitive ability is a significant predictor of children's cognitive ability; moreover, it explains one sixth of the socio-economic gap in those skills, even after controlling for a rich set of demographic, attitudinal and behavioural factors. Despite the importance of parental cognitive ability in explaining children's cognitive ability, however, the addition of such typically unobserved characteristics does not alter our impression of the relative importance of other factors in explaining the socio-economic gap in cognitive skills. This is reassuring for studies that are unable to control for parental cognitive ability.

Does Publicly Provided Health Insurance Improve the Health of Low-Income Children in the United States

In this study we analyze the effect of Medicaid on children's heath. We examine the effect of Medicaid on a variety of health outcomes using two data sources: the National Health Interview Surveys (NHIS) and the Nationwide Inpatient Sample (NIS) of hospital discharges. Using the NHIS, we examine the effect of Medicaid participation on maternal ratings of child health and maternal reports of the number of bed days in the past year (i.e. morbidity). The NIS data was used to examine the effect of Medicaid program expansions on the incidence of ambulatory care sensitive (ACS) discharges. ACS discharges are known to be sensitive to medical intervention and are objective measures of children's health. The results of this paper provide at best weak support for the hypothesis that Medicaid improves the health of low-income children.

Family Cap Provisions and Changes in Births and Abortions

As part of welfare reform efforts in the 1990s, twenty-three states implemented family caps, provisions that deny or reduce cash assistance to welfare recipients who have additional births. We use birth and abortion records from 24 states to estimate effects of family caps on birth and abortion rates. We use age, marital status and completed schooling to identify women at high risk for use of public assistance, and parity (number of previous live births) to identify those most directly affected by the family cap. In family cap states, birth rates fell more and abortion rates rose more among high-risk women with at least one previous live birth compared to similar childless women, consistent with an effect of the family cap. However, this parity-specific pattern of births and abortions also occurred in states that implemented welfare reform with no family cap. Thus, the effects of welfare reform may have differed between mothers and childless women, but there is little evidence of an independent effect of the family cap.

Child poverty in the UK since 1998-99: lessons from the past decade

As a result of the Child Poverty Act (2010), current and future governments are committed to reducing the rate of relative income child poverty in the UK to 10% by 2020-21. This paper looks in detail at the progress made towards this goal under the previous Labour administrations. Direct tax and benefit reforms are very important in explaining at least three things: the large overall reduction in child poverty since 1998-99; the striking slowdown in progress towards the child poverty targets between 2004-05 and 2007-08; and some of the variation in child poverty trends between different groups of children. However, some of the child poverty-reducing impact of those reforms acted simply to stop child poverty rising as real earnings grew over the period, which increases median income and thus the relative poverty line. The performance of parents in the labour market is important too: between regions, parental employment and child poverty trends are closely related; the overall reduction in child poverty since 1998-99 has been helped by higher lone parent employment rates; and the overall rise in child poverty since 2004-05 has been most concentrated on children of one-earner couples, whose real earnings have fallen.