Microscopic mass formulae

By assuming the existence of a pseudopotential smooth enough to do Hartree-Fock variations and good enough to describe nuclear structure, we construct mass formulae that rely on general scaling arguments and on a schematic reading of shell model calculations. Fits to 1751 known binding energies for N,Z$\geq 8$ lead to RMS errors of 614 keV with 14 parameters and 388 keV with 28 parameters. The latter is easily reduced to a 20 parameter form at 423 keV.Comment: 6 pages, REVTEX dialec

Dams

The construction of large dams is one of the most costly and controversial forms of public infrastructure investment in developing countries, but little is known about their impact. This paper studies the productivity and distributional effects of large dams in India. To account for endogenous placement of dams we use GIS data and the fact that river gradient affects a district's suitability for dams to provide instrumental variable estimates of their impact. We find that, in a district where a dam is built, agricultural production does not increase but poverty does. In contrast, districts located downstream from the dam benefit from increased irrigation and see agricultural production increase and poverty fall. Overall, our estimates suggest that large dam construction in India is a marginally cost-effective investment with significant distributional implications, and has, in aggregate, increased poverty.

Intrahousehold Resource Allocation in Cote d'Ivoire: Social Norms, Separate Accounts and Consumption Choices

We study resource allocation within households in C“te d'Ivoire. In C“te d'Ivoire, as in much of Africa, husbands and wives farm separate plots, and there is some specialization by gender in the crops that are grown. These different crops are differentially sensitive to particular kinds of rainfall shocks. We find that conditional on overall levels of expenditure, the composition of household expenditure is sensitive to the gender of the recipient of a rainfall shock. For example, rainfall shocks associated with high yields of women's crops shift expenditure towards food. Strong social norms constrain the use of profits from yam cultivation, which is carried out almost exclusively by men. In line with these norms, we find that rainfall-induced fluctuations in income from yams are transmitted to expenditures on education and food, not to expenditures on private goods (like alcohol and tobacco). We reject the hypothesis of complete insurance within households, even with respect to publicly observable weather shocks. Different sources of income are allocated to different uses depending upon both the identity of the income earner and upon the origin of the income.

The Role of Information and Social Interactions in Retirement Plan Decisions: Evidence from a Randomized Experiment

This paper analyzes a randomized experiment to shed light on the role of information and social interactions in employees' decisions to enroll in a Tax Deferred Account (TDA) retirement plan within a large university. The experiment encouraged a random sample of employees in a subset of departments to attend a benefits information fair organized by the university, by promising a monetary reward for attendance. The experiment more than tripled the attendance rate of these treated individuals (relative to controls), and doubled that of untreated individuals within departments where some individuals were treated. TDA enrollment 5 and 11 months after the fair was significantly higher in departments where some individuals were treated than in departments where nobody was treated. However, the effect on TDA enrollment is almost as large for individuals in treated departments who did not receive the encouragement as for those who did. We provide three interpretations, differential treatment effects, social network effects, and motivational reward effects, to account for these results.

Aging and Death under a Dollar a Day

This paper uses household survey data form several developing countries to investigate whether the poor (defined as those living under $1 or$2 dollars a day at PPP) and the non poor have different mortality rates in old age. We construct a proxy measure of longevity, which is the probability that an adult's mother and father are alive. The non-poor's mothers are more likely to be alive than the poor's mothers. Using panel data set for Indonesia and Vietnam, we also find that older adults are significantly more likely to have died five years later if they are poor. The direction of causality is unclear: the poor may be poor because they are sick (and thus more likely to die), or they could die because they are poor.

How Much Should We Trust Differences-in-Differences Estimates?

Most Difference-in-Difference (DD) papers rely on many years of data and focus on serially correlated outcomes. Yet almost all these papers ignore the bias in the estimated standard errors that serial correlation introduce4s. This is especially troubling because the independent variable of interest in DD estimation (e.g., the passage of law) is itself very serially correlated, which will exacerbate the bias in standard errors. 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, we use OLS to compute the DD estimate of its 'effect' as well as the standard error for this estimate. The standard errors are severely biased: with about 20 years of data, DD estimation finds an 'effect' significant at the 5% level of up to 45% of the placebo laws. Two very simple techniques can solve this problem for large sample sizes. The first technique consists in collapsing the data and ignoring the time-series variation altogether; the second technique is to estimate standard errors while allowing for an arbitrary covariance structure between time periods. We also suggest a third technique, based on randomization inference testing methods, which works well irrespective of sample size. This technique uses the empirical distribution of estimated effects for placebo laws to form the test distribution.

Using Randomization in Development Economics Research: A Toolkit

This paper is a practical guide (a toolkit) for researchers, students and practitioners wishing to introduce randomization as part of a research design in the field. It first covers the rationale for the use of randomization, as a solution to selection bias and a partial solution to publication biases. Second, it discusses various ways in which randomization can be practically introduced in a field settings. Third, it discusses designs issues such as sample size requirements, stratification, level of randomization and data collection methods. Fourth, it discusses how to analyze data from randomized evaluations when there are departures from the basic framework. It reviews in particular how to handle imperfect compliance and externalities. Finally, it discusses some of the issues involved in drawing general conclusions from randomized evaluations, including the necessary use of theory as a guide when designing evaluations and interpreting results.