A Combined D.C. Optimization—Ellipsoidal Branch-and-Bound Algorithm for Solving Nonconvex Quadratic Programming Problems

In this paper we propose a new branch-and-bound algorithm by using an ellipsoidal partition for minimizing an indefinite quadratic function over a bounded polyhedral convex set which is not necessarily given explicitly by a system of linear inequalities and/or equalities. It is required that for this set there exists an efficient algorithm to verify whether a point is feasible, and to find a violated constraint if this point is not feasible. The algorithm is based upon the fact that the problem of minimizing an indefinite quadratic form over an ellipsoid can be efficiently solved by some available (polynomial and nonpolynomial time) algorithms. In particular, the d.c. (difference of convex functions) algorithm (DCA) with restarting procedure recently introduced by Pham Dinh Tao and L.T. Hoai An is applied to globally solving this problem. DCA is also used for locally solving the nonconvex quadratic program. It is restarted with current best feasible points in the branch-and-bound scheme, and improved them in its turn. The combined DCA-ellipsoidal branch-and-bound algorithm then enhances the convergence: it reduces considerably the upper bound and thereby a lot of ellipsoids can be eliminated from further consideration. Several numerical experiments are given.     

Welfare Reform and Asset Accumulation: Asset Limit Changes,Financial Assets,and Vehicle Ownership*

Objective. Over the past decade, federal and state governments have substantially liberalized asset limits in welfare. This article examines whether this policy change promotes asset accumulation among the target population of actual and potential welfare recipients. Methods. Utilizing household data from the Panel Study of Income Dynamics as well as state data, this study employs a difference‐in‐difference approach in order to determine whether state asset limits affect the target population's financial and vehicle asset accumulation. This study develops a new policy measure that considers the time period following the adoption of liberalized asset limits. Results. Analysis results suggest that increased asset limits may have successfully encouraged the target population's asset accumulation. The earlier a state raised its asset limit, the more likely welfare recipients were to accumulate financial assets and to possess bank accounts. Conclusion. It is recommended to liberalize asset eligibility rules to promote long‐term economic advancement of poor households.     

Insights on medical tourism: markets as networks and the role of strong ties

Despite a huge amount of speculation and expectation surrounding medical tourism, hard empirical evidence is only now beginning to emerge. This paper widens the focus of discussion by contrasting two country experiences (UK and Korea) which on the surface illustrate the diversity of medical tourism and little else. However, considered more comparatively, the accounts contribute toward wider, albeit tentative, theoretical understandings, and insights. The paper is drawn from two broad programs of empirical study conducted over three years in UK and Korea, respectively. The article is structured in three parts: first, a brief overview of policy, legislative, and accreditation frameworks that exist to govern medical tourist flows. Second, we present evidence around flows, demographics, treatment, and medical tourism for Korea and UK (both for supply and demand). Third, we examine conceptual and theoretical implications of this evidence. We argue that viewing medical tourism as a global market is problematic; some medical tourist markets are best viewed as networks with long-term exchange relationships; some specific areas of activity do function more strongly as price-related; decision making around medical tourism frequently involves a range of information and social networks (economic action as embedded social structure); and medical tourism is a function of globalization.     

Comparing the Survival of Two Groups with an Intermediate Clinical Event

Consider a subject entered on a clinicaltrial in which the major endpoint is a time metric such as deathor time to reach a well defined event. During the observationalperiod the subject may experience an intermediate clinical event.The intermediate clinical event may induce a change in the survivaldistribution. We consider models for the one and two sample problem.The model for the one sample problem enables one to test if theoccurrence of the intermediate event changed the survival distribution.This models provides a way of carrying out non-randomized clinicaltrial to determine if a therapy has benefit. The two sample problemconsiders testing if the probability distributions, with andwithout an intermediate event, are the same. Statistical testsare derived using a semi-Markov or a time dependent mixture model.Simulation studies are carried out to compare these new procedureswith the log rank, stratified log rank and landmark tests. Thenew tests appear to have uniformly greater power than these competitortests. The methods are applied to a randomized clinical trialcarried out by the Aids Clinical Trial Group (ACTG) which comparedlow versus high doses of zidovudine (AZT).     

Small-dollar children's saving accounts and children's college outcomes by race

This is paper three of four in the Small-Dollar Children Accounts series that studies the relationship between children's small dollar savings accounts and college enrollment and graduation. The series uses different subsamples to examine three important research questions: (a) Are children with savings of their own more likely to attend or graduate from college? (b) Does dosage (no account, only basic savings, savings designated for school of less than $1, $1 to $499, or $500 or more) matter? And (c) is designating for school more predictive of college enrollment or graduation than having basic undesignated savings alone? Using propensity score weighted data from the Panel Study of Income Dynamics and its supplements we created multi-treatment dosages of savings accounts and amounts to answer these questions separately for black (n = 404) and white (n = 453) children. White children's savings are not significantly related to their college outcomes. Differently, compared to black children without savings accounts, black children are three times more likely to enroll in college when they have school savings of less than $1 and six times more likely when they have school savings of $1 to $499. Further, black children with school savings of $1 to $499 are four times more likely to graduate from college and black children with school savings of $500 or more are three-and-a-half times more likely to graduate from college, compared to those with no savings account. We suggest Child Development Accounts (CDAs) may be a promising tool for helping black children get to and through college.     

Households' Perceived Personal Risk and Responses in a Multihazard Environment

This study proposed and tested a multistage model of household response to three hazards—flood, hurricane, and toxic chemical release—in Harris County Texas. The model, which extends Lindell and Perry's (1992, 2004) Protective Action Decision Model, proposed a basic causal chain from hazard proximity through hazard experience and perceived personal risk to expectations of continued residence in the home and adoption of household hazard adjustments. Data from 321 households generally supported the model, but the mediating effects of hazard experience and perceived personal risk were partial rather than complete. In addition, the data suggested that four demographic variables—gender, age, income, and ethnicity—affect the basic causal chain at different points.     

The Effects of Depressive Symptoms on Work Activities and Welfare Exit of Welfare Recipients in Korea1

The purpose of this research is to examine the link between depressive symptoms of welfare recipients and their work activity and welfare exit using a secondary dataset, entitled the Korean Welfare Panel Study. In 2000, the National Basic Livelihood Security System (NBLSS) was introduced to (i) ensure a basic standard of living for households in poverty, and (ii) promote work activity and welfare exit of the recipients. A considerable body of literature has reported that the policy outcome of the NBLSS is not a success. However, the reason for the low success rate is unclear. In contrast to studies in the USA, few studies in Korea investigated the effect of depression on welfare‐to‐work transitions. To bridge the gap in the literature, we examine the association between depression, work activity, and welfare exit using a logistic regression analytic method. The analytic results show that the level of depression (total score on the Center for Epidemiological Studies Depression Scale) was negatively associated with welfare recipients’ work activity and welfare exit, suggesting that depressive symptoms may be a significant barrier to promoting economic self‐sufficiency. Implications of the study findings are further discussed.     

Mental Health Conditions Among North Korean Female Refugee Victims of Sexual Violence

The study aims to examine the negative effects of sexual violence on North Korean (NK) female refugees in South Korea. Although the prevalence of sexual violence victimization is extremely high and mental health problems are serious among these refugees, little to no research has been done on the relationship between sexual violence and mental health among these women. The mental health conditions of two groups of women (sexual violence victims and those who have not experienced sexual violence) were compared using ANCOVA analyses. The results show that suicidal ideation and alcohol use are significantly more prevalent in the sexual violence group than in the non‐sexual violence group. The women who had experienced sexual violence in particular should be provided with more professional and sustained treatment and management services. The government must improve the effectiveness of existing policies related to suicide and the drinking culture in South Korea.     

Underlying and multiple causes of death related to smoking

Although smoking has been linked to various causes of death, there is no systematic account of the underlying and multiple cause-of-death distributions associated with various smoking statuses. We analyze such patterns by age and gender for the USA in 1986. Our study is based on a one-percent random sample of decedents 25 and over in the USA for whom survey data from informants were linked to death certificate data. Smoking is related to several underlying causes of death, the most common being circulatory diseases. Lung cancer is less prevalent than circulatory diseases or other cancers among ever smokers. Multiple medical conditions are common for both smokers and nonsmokers, but particular combinations vary among persons with different smoking statuses. Former smokers who quit soon before death and were under frequent medical care are most likely to have had lung cancer. Amount of smoking is tied to variations in cause-of-death patterns. Differences by age and gender are not substantial, although other cancers appear frequently for both smokers and non-smokers among women. The distribution of medical causes of death for ever smokers is not radically different from that of never smokers. However, differences in cause patterns are seen when smoking statuses are detailed by amount of smoking and timing of quitting. These similarities and differences in cause patterns must be related to the fundamental fact that the average smoker will die earlier than the average nonsmoker. Such findings should especially influence programs for diseases whose links to smoking have been underestimated.