Incrementing Bipartite Digraph Edge-Connectivity

This paper solves the problem of increasing the edge-connectivity of a bipartite digraph by adding the smallest number of new edges that preserve bipartiteness. A natural application arises when we wish to reinforce a 2-dimensional square grid framework with cables. We actually solve the more general problem of covering a crossing family of sets with the smallest number of directed edges, where each new edge must join the blocks of a given bipartition of the elements. The smallest number of new edges is given by a min-max formula that has six infinite families of exceptional cases. We discuss a problem on network flows whose solution has a similar formula with three infinite families of exceptional cases. We also discuss a problem on arborescences whose solution has five infinite families of exceptions. We give an algorithm that increases the edge-connectivity of a bipartite digraph in the same time as the best-known algorithm for the problem without the bipartite constraint: O(km log n) for unweighted digraphs and O(nm log (n ²/m)) for weighted digraphs, where n, m and k are the number of vertices and edges of the given graph and the target connectivity, respectively.     

Resisting Smoking When a Best Friend Smokes: Do Intrapersonal and Contextual Factors Matter?

This longitudinal study examines individual differences in the tendency to initiate (N = 4,612) and escalate (N = 2,837) smoking when adolescents gain a best friend who smokes. Potential moderating factors include self-esteem, depression, problem behavior, school and family bonds, and household access to cigarettes. In addition to acquiring a smoking best friend, initiation was predicted by trouble at school, household access, poorer grades and delinquency, whereas escalation was predicted by depressive symptoms. There was little evidence that the examined individual difference factors moderate the association between gaining a smoking best friend and increased adolescent smoking. Results point to the challenges of identifying factors that may lead adolescents to be more or less susceptible to the influence of pro-smoking friends.     

Evaluating retailer behavior in preventing youth access to harmful legal products a feasibility test

This article reports results from a feasibility study of a community effort to reduce the availability of legal products that youth can use to get high. The study evaluated the potential of youth purchase attempts to detect actual changes in retail availability of harmful legal products. These results were triangulated with self-reports from retailers about their own policies and practices. Before the intervention, less than half of retailers reported using any of six possible strategies identified as ways to reduce youth access to harmful products, and less than 8% of baseline youth attempts to purchase potentially harmful legal products were refused or questioned. After the low-dosage intervention, retailers reported increased use of three strategies and a statistically significant increase in the percentage of purchase attempts that were either questioned or refused by retail clerks. These findings (a) demonstrate the potential feasibility of retailer-focused environmental strategies and (b) support continued use of youth purchase attempts as a measure of actual retailer behavior.     

CAN SCHOOL SPORTS REDUCE RACIAL GAPS IN TRUANCY AND ACHIEVEMENT?

While existing research supports that participation in high‐school athletics is associated with better education and labor‐market outcomes, the mechanisms through which these benefits accrue are not well established. Using individual microdata collected daily, and team‐specific schedules, we retrieve estimates of the causal effect of high‐school athletic participation on absenteeism, suggesting that participation decreases absences, driven primarily by reductions in unexcused absences in boys. There are also strong game‐day effects in truancy, in both boys and girls, with truancy declines on game days more than offset by subsequent absenteeism. Important heterogeneity by race, gender, and family structure may serve to substantially reduce racial gaps in truancy and achievement. (JEL I21, L83)     

Is consanguinity an impediment to child development?

Marriages between blood relatives—also known as consanguineous unions—are widespread in North Africa, Central and West Asia, and South Asia. Researchers have suggested that consanguinity has adverse effects on child development, but assessing its impact is not straightforward, as the decision to marry a relative might be endogenous to other socio-economic factors. Using a unique data set collected in rural Pakistan, this paper assesses the extent to which consanguinity is linked to children’s cognitive and physical development. It exploits grandfathers’ land ownership (current and past) and maternal grandparent mortality to identify the effect of endogenous consanguinity on child development. Children born into consanguineous unions have lower cognitive scores, lower height-for-age, and a higher likelihood of being severely stunted. More importantly, adverse effects are greater after accounting for the endogeneity of consanguinity, suggesting that impacts on child development are substantial, and likely to be larger than suggested in previous studies.     

INVENTORY DECISIONS UNDER INFLATIONARY CONDITIONS

The standard approach to inventory policy ignores the effect of inflation. This paper investigates a model that includes both inflationary trends and time discounting. The paper compares this model with the standard EOQ model and the analysis for a one-time change, found in previous literature.