On the validity of retrospective assessments of pregnancy intention

Information on pregnancy intention is often gathered retrospectively (after the birth of a child). This article investigates whether the retrospective assessment of pregnancy intention leads to biased estimates of the extent or consequences of unintended fertility. Comparisons are made between pregnancy intentions ascertained during pregnancy and after birth using data from the National Longitudinal Survey of Youth. To address the bias caused by selective recognition or acknowledgment of pregnancy, we used the longitudinal feature of the data to determine actual pregnancy status at the time of interviews, which, in turn, was used as an instrumental variable for the retrospective (versus prospective) reporting of pregnancy intention. After correction for selective pregnancy recognition, we found no evidence that the retrospective assessment of pregnancy intention produces misleading estimates of either the number or the consequences of unintended births. This finding is supported by additional analyses of a small subsample of women for whom information on pregnancy intention was collected both during pregnancy and after birth.     

Employment status,material hardship,and mental health among low-income working-age adults in South Korea

The current study examines the associations between employment status and mental health and the mediating role of material hardship among low-income households in South Korea. This study uses regression models with a rich set of control variables and lagged dependent variable models with a nationally representative sample of 1113 low-income working-age household heads from the Korean Welfare Panel Study (KOWEPS). We find that the nonstandard employment and unemployment statuses are associated with a higher level of depression and a lower level of self-esteem, when compared to a standard employment status. These negative associations are partially mediated by an increased material hardship risk. Policy implications to improve employment conditions and mitigate material hardship are discussed.     

Recommended Reference Values for Risk Assessment of Oral Exposure to Copper

The U.S. Environmental Protection Agency's (EPA) Integrated Risk Information System (IRIS) database, the authoritative source of U.S. risk assessment toxicity factors, currently lacks an oral reference dose (RfD) for copper. In the absence of such a value, various health-based reference values for copper are available for use in risk assessment. We summarize the scientific bases and differences in assumptions among key reference values for ingested copper to guide selection of appropriate values for risk assessment. A comprehensive review of the scientific literature best supports the oral RfD of 0.04 mg/kg body weight/day derived by EPA from their Drinking Water Action Level. This value is based on acute gastrointestinal effects but is further supported by broader analysis of copper deficiency and toxicity.     

MODELING LEARNING CURVE AND LEARNING COMPLEMENTARITY FOR RESOURCE ALLOCATION AND PRODUCTION SCHEDULING*

Research on learning effects in mathematical programming models for optimum resource allocation has called attention to the difficulty in solving such models in their original nonlinear form. In this paper, systematically varying sizes of linear segments are designed to approximate productivity changes along the learning curve, and a single separable linear programming model is developed. With production complementarity and learning transmission between products, a more realistic resource allocation and production scheduling problem emerges. Two cases of learning transmissions are considered, and the model design process, which defines a decision problem that can be solved by a simplex algorithm, is demonstrated.