Preliminary evidence regarding the hypothesis that the sex ratio at sexual maturity may affect longevity in men

In human populations, variation in mate availability has been linked to various biological and social outcomes, but the possible effect of mate availability on health or survival has not been studied. Unbalanced sex ratios are a concern in many parts of the world, and their implications for the health and survival of the constituent individuals warrant careful investigation. We indexed mate availability with contextual sex ratios and investigated the hypothesis that the sex ratio at sexual maturity might be associated with long-term survival for men. Using two unique data sets of 7,683,462 and 4,183 men who were followed for more than 50 years, we found that men who reached their sexual maturity in an environment with higher sex ratios (i. e., higher proportions ofreproductively ready men) appeared to suffer higher long-term mortality risks than those in an environment with lower sex ratios. Mate availability at sexual maturity may be linked via several biological and social mechanisms to long-term survival in men.     

Wives and ex-wives: A new test for homogamy bias in the widowhood effect

Increased mortality following the death of a spouse (the “widowhood effect”) may be due to (1) causation, (2) bias from spousal similarity (homogamy), or (3) bias from shared environmental exposures. This article proposes new tests for bias in the widowhood effect by examining husbands, wives, and ex-wives in a longitudinal sample of over 1 million elderly Americans. If the death of an ex-wife has no causal effect on the mortality of her husband, then an observed association between the mortality of an ex-wife and her husband may indicate bias, while the absence of an effect of an ex-wife’s death on her husband’s mortality would discount the possibility of homogamy bias (and also of one type of shared-exposure bias). Results from three empirical tests provide strong evidence for an effect of a current wife’s death on her husband’s mortality yet no statistically signifi cant evidence for an effect of an ex-wife’s death on her husband’s mortality. These results strengthen the causal interpretation of the widowhood effect by suggesting that the widowhood effect is not due to homogamy bias to any substantial degree.     

Born to lead? A twin design and genetic association study of leadership role occupancy

We address leadership emergence and the possibility that there is a partially innate predisposition to occupy a leadership role. Employing twin design methods on data from the National Longitudinal Study of Adolescent Health, we estimate the heritability of leadership role occupancy at 24%. Twin studies do not point to specific genes or neurological processes that might be involved. We therefore also conduct association analysis on the available genetic markers. The results show that leadership role occupancy is associated with rs4950, a single nucleotide polymorphism (SNP) residing on a neuronal acetylcholine receptor gene (CHRNB3). We replicate this family-based genetic association result on an independent sample in the Framingham Heart Study. This is the first study to identify a specific genotype associated with the tendency to occupy a leadership position. The results suggest that what determines whether an individual occupies a leadership position is the complex product of genetic and environmental influences, with a particular role for rs4950.     

FIXED-EFFECTS METHODS FOR THE ANALYSIS OF NONREPEATED EVENTS

For repeated events, fixed-effects regression methods—which control for all stable covariates—can be implemented by doing Cox regression with stratification on individuals. For nonrepeated events, we consider the use of conditional logistic regression to estimate fixed-effects models with discrete-time data. Known in the epidemiological literature as the case-crossover design, this method fails when any covariate is a monotonic function of time. Hence, no control for time itself can be included, leading to potentially spurious estimates. As an alternative, we consider the case-time-control method for estimating the effect of a dichotomous predictor. This method allows for the introduction of a control for time by reversing the role of the dependent and independent variables. In contrast to earlier work, we show that the method can be applied to data that contain only uncensored cases, and that it is possible to control for additional covariates, both categorical and quantitative. Simulation studies indicate that the case-time-control method is substantially superior to the case-crossover method and to conventional logistic regression. The methods are illustrated by estimating the effect of a wife's death on the hazard of death for her husband.     

Product Positioning Using a Self‐Organizing Map and the Rings of Influence

In this article, we propose a new product positioning method based on the neural network methodology of a self‐organizing map. The method incorporates the concept of rings of influence, where a firm evaluates individual consumers and decides on the intensity to pursue a consumer, based on the probability that this consumer will purchase a competing product. The method has several advantages over earlier work. First, no limitations are imposed on the number of competing products and second, the method can position multiple products in multiple market segments. Using simulations, we compare the new product positioning method with a quasi‐Newton method and find that the new method always approaches the best solution obtained by the quasi‐Newton method. The quasi‐Newton method, however, is dependent on the initial positions of the new products, with the majority of cases ending in a local optimum. Furthermore, the computational time required by the quasi‐Newton method increases exponentially, while the time required by the new method is small and remains almost unchanged, when the number of new products positioned increases. We also compute the expected utility that a firm will provide consumers by offering its products. We show that as the intensity with which a firm pursues consumers increases, the new method results in near‐optimal solutions in terms of market share, but with higher expected utility provided to consumers when compared to that obtained by a quasi‐Newton method. Thus, the new method can serve as a managerial decision‐making tool to compare the short‐term market share objective with the long‐term expected utility that a firm will provide to consumers, when it positions its products and intensifies its effort to attract consumers away from competition.     

A methodology for identifying married couples in medicare data: Mortality, morbidity, and health care use among the married elderly

Wedescribe a method for the development of cohorts of up to three quarters of the 14 million married couples aged 65 and over in the United States. The health care experiences, illness histories, and mortality of these identified couples can be assessed longitudinally using Medicare data. We summarize strengths and limitations of using data from Medicare administrative records for the study of marriage, health, and aging. We illustrate the method by demonstrating substantial differences in survival in a cohort of hospice patients as a function of not only the patient's own diagnosis and illness burden but also the patient's spouse's illness burden.