Confidence intervals for the symmetry point: an optimal cutpoint in continuous diagnostic tests

Continuous diagnostic tests are often used for discriminating between healthy and diseased populations. For this reason, it is useful to select an appropriate discrimination threshold. There are several optimality criteria: the North‐West corner, the Youden index, the concordance probability and the symmetry point, among others. In this paper, we focus on the symmetry point that maximizes simultaneously the two types of correct classifications. We construct confidence intervals for this optimal cutpoint and its associated specificity and sensitivity indexes using two approaches: one based on the generalized pivotal quantity and the other on empirical likelihood. We perform a simulation study to check the practical behaviour of both methods and illustrate their use by means of three real biomedical datasets on melanoma, prostate cancer and coronary artery disease. Copyright © 2016 John Wiley & Sons, Ltd.     

Properties and applications of the Poisson-reciprocal inverse Gaussian distribution

The barely known continuous reciprocal inverse Gaussian distribution is used in this paper to introduce the Poisson-reciprocal inverse Gaussian discrete distribution. Several of its most relevant statistical properties are examined, some of them directly inherited from the reciprocal of the inverse Gaussian distribution. Furthermore, a mixed Poisson regression model that uses the reciprocal inverse Gaussian as mixing distribution is presented. Parameters estimation in this regression model is performed via an EM type algorithm. In light of the numerical results displayed in the paper, the distributions introduced in this work are competitive with the classical negative binomial and Poisson-inverse Gaussian distributions.     

Prevalence and Correlates of Sex Exchange Among a Nationally Representative Sample of Adolescents and Young Adults

The present study examines prevalence and correlates of exchanging sex for drugs, money, food shelter, or other favors (sex exchange) among a nationally representative sample of youth and young adults. Adolescents and young adults (n = 11,620, 53% female, 47% male) from the National Longitudinal Study of Adolescent Health were used for the current sample. Participants completed in-home interviews at both waves. Results revealed that sex exchange was reported by 4.9% (n = 569) of the population in wave 2 or wave 3, and 4.6% (n = 26) of those who exchanged sex did so at both waves. More males reported exchanging sex than females (n = 332 versus n = 237). Respondents who reported child sexual abuse were more likely to exchange sex (95% CI 2.51–4.28, p < .05) than respondents who reported any other form of child abuse. Both males and females who engaged in sex exchange were at greater risk for sexually transmitted infections; however, the odds of ever exchanging sex were highest among males who ever had gonorrhea (OR = 6.2; 95% CI 3.75–10.3). Although sex exchange has been studied extensively among homeless and runaway youth, the current study reveals sex exchange also occurs in the general population.     

A cost valuation model based on a stochastic representation of the IPAT equation

Within the framework of models for human-driven environmental impact based on the IPAT equation, we develop a model for the evolution of impact (expressed in terms of carbon dioxide emissions) and for the valuation of the economic cost associated to its reduction. We use a stochastic representation of the IPAT equation that is alternative to the STIRPAT model. This first step leads to a stochastic differential equations model that describes trends in carbon dioxide emissions on the basis of economic and demographic dynamics. As an example, we estimate the model parameters for the United States. We then use this framework to build a model for the assessment of the economic costs related to a reduction of carbon dioxide emissions for a country committed to respect an international agreement, such as the Kyoto protocol. In particular, we show that the adherence to an environmental treaty may be traced back to a problem of cost valuation and to a decision under risk. This allows us to use the mathematical tools that have been developed in quantitative finance, in the context of option pricing, to determine the expected investment that is required to reduce the emissions of a country by a certain amount and within a well-defined temporal frame.

People and Pixels 20 years later: the current data landscape and research trends blending population and environmental data

Population and Environment - In 1998, the National Research Council published People and Pixels: Linking Remote Sensing and Social Science. The volume focused on emerging research linking changes...     

Social change,population policies,and fertility decline in Colombia and Venezuela

This paper takes a comparative case-study approach to examine the social and policy correlates of fertility decline. The analysis compares fertility behavior across a mature and young cohort of women in Colombia and Venezuela, two countries that experienced rapid demographic change under dissimilar socioeconomic and population policy conditions. Based on the distinction between birth-spacing and birth-stopping behavior the analysis tests several propositions derived from the adaptation and innovation explanations of fertility decline. Results show that fertility regulation at low parities was largely absent among mature women in both countries, representing an innovative behavior among younger women. The introduction of fertility control, however, was highly dependent on women's socioeconomic position, particularly their educational and occupational characteristics. The strong family planning programs in Colombia resulted in a more rapid extension of contraceptive use, particularly female sterilization, and stopping behavior after two children relative to Venezuela. Results highlight the diversity of conditions under which fertility can decline in developing countries and the importance of family planning and other policy initiatives to understanding the different pathways towards lower fertility.     

Intergenerational fertility among hispanic women: New evidence of immigrant assimilation

In recent decades, rapid growth of the U.S. Hispanic population has raised concerns about immigrant adaptation, including fertility. Empirical research suggests that Hispanics, especially Mexicans, might not be following the historical European pattern of rapid intergenerational fertility decline (and convergence toward native levels). If confirmed, continued high Hispanic fertility could indicate a broader lack of assimilation into mainstream American society. In this paper, we reexamine the issue of Hispanic and Mexican fertility using an approach that combines biological and immigrant generations to more closely approximate a comparison of immigrant women with those of their daughters’ and granddaughters’ generation. Contrary to cross-sectional results, our new analyses show that Hispanic and Mexican fertility is converging with that of whites, and that it is similarly responsive to period conditions and to women’s level of education. In addition, we employ a mathematical simulation to illustrate the conditions under which cross-sectional analyses can produce misleading results. Finally, we discuss the import of the fertility convergence we document for debates about immigrant assimilation.     

A Flexible Bayesian Model for Estimating Subnational Mortality

Reliable subnational mortality estimates are essential in the study of health inequalities within a country. One of the difficulties in producing such estimates is the presence of small populations among which the stochastic variation in death counts is relatively high, and thus the underlying mortality levels are unclear. We present a Bayesian hierarchical model to estimate mortality at the subnational level. The model builds on characteristic age patterns in mortality curves, which are constructed using principal components from a set of reference mortality curves. Information on mortality rates are pooled across geographic space and are smoothed over time. Testing of the model shows reasonable estimates and uncertainty levels when it is applied both to simulated data that mimic U.S. counties and to real data for French départements. The model estimates have direct applications to the study of subregional health patterns and disparities.     

Hispanic Familism Reconsidered

Familism has been described as a cultural trait that might explain why the fertility of Hispanic women remains higher than non‐Hispanic white women. Still, few studies have analyzed group differences in childbearing attitudes. This article focuses on two dimensions of childbearing orientation: social value of children and fertility intentions. Using the National Survey of Family Growth, we find limited support for the idea that familism undergirds differentials in fertility between native‐born Hispanics and whites. However, for foreign‐born Hispanics, there are some differences in the perceived value of children compared with whites, and these differences could contribute to fertility differentials.