PARC Departmental Papers
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Publication Natural Selection in a Contemporary Human Population(2009-10-26) Ewbank, DouglasOur aims were to demonstrate that natural selection is operating on contemporary humans, predict future evolutionary change for specific traits with medical significance, and show that for some traits we can make short-term predictions about our future evolution. To do so, we measured the strength of selection, estimated genetic variation and covariation, and predicted the response to selection for women in the Framingham Heart Study, a project of the National Heart, Lung, and Blood Institute and Boston University that began in 1948. We found that natural selection is acting to cause slow, gradual evolutionary change. The descendants of these women are predicted to be on average slightly shorter and stouter, to have lower total cholesterol levels and systolic blood pressure, to have their first child earlier, and to reach menopause later than they would in the absence of evolution. Selection is tending to lengthen the reproductive period at both ends. To better understand and predict such changes, the design of planned large, long-term, multicohort studies should include input from evolutionary biologists.Publication Educational differences in all-cause mortality Evidence from Bulgaria, Finland and the United States(2008-12-10) Kohler, Iliana; Martikainen, Pekka; Smith, Kirsten P; Elo, Irma T.Using life table measures, we compare educational differentials in all-cause mortality at ages 40 to 70 in Bulgaria to those in Finland and the United States. Specifically, we assess whether the relationship between education and mortality is modified by marital status. Although high education and being married are associated with lower mortality in all three countries, absolute educational differences tend to be smaller among married than unmarried individuals. Absolute differentials by education are largest for Bulgarian men, but in relative terms educational differences are smaller among Bulgarian men than in Finland and the U.S. Among women, Americans experience the largest education-mortality gradients in both relative and absolute terms. Our results indicate a particular need to tackle health hazards among poorly educated men in countries in transition.Publication Childhood Predictors of Late-Life Diabetes: The Case of Mexico(2005-09-01) Kohler, Iliana V; Soldo, Beth JWe investigated the interplay between characteristics of early childhood circumstances and current socioeconomic conditions and health, focusing specifically on diabetes in mid and late life in Mexico. The analysis used data from the 2001 Mexican Health and Aging Study (MHAS), a large nationally representative study of Mexicans born before 1950. We analyzed the extent to which childhood conditions, such as exposure to infectious diseases, a poor socioeconomic environment, and parental education, affect the risk of diabetes in later life. Our results indicate that individuals age 50 and older who experienced serious health problems before age 10 have a higher risk of having late-life diabetes. There is a significant inverse relationship between maternal education and diabetes in late life of adult offspring. Individuals with better educated mothers have a lower risk of being diabetic after age 50. This relationship remains after controlling for other childhood and adult risk factors.Publication When Mental Health Becomes Health: Age and the Shifting Meaning of Self-evaluations of General Health(2005-09-01) Schnittker, JasonSelf-evaluations of general health are among the most widely-used measures of health status in research on the need for and outcomes of medical care. Yet, researchers know little about the psychological processes behind them. This study looks at whether such evaluations, often referred to as self-rated health, shift in what they measure as individuals age. Although several perspectives point to age-related shifts, few researchers have explicitly tested these perspectives against each other. The study tests several competing hypotheses using a large, nationally representative, and longitudinal data set. The results suggest two countervailing trends. First, the correspondence between functional limitations and self-rated health declines, especially after the age of 50. Similarly, the correspondence between a variety of chronic conditions and self-rated health, while strong, declines precipitously. Both of these findings are consistent with the idea that individuals evaluate their health through a process of social comparison and, in so doing, are able to maintain an elevated sense of general health even as they age. Yet, the results also suggest that the correspondence between depressive symptoms and self-rated health increases steadily throughout the life course. Indeed, after the age of 74, the correspondence between self-rated health and some common symptoms of depression becomes stronger than the correspondence between self-rated health and several chronic, and often fatal, somatic conditions. The implications of this crossover for both theory and policy are discussed. Among other things, the crossover has important implications for the detection and treatment of depressive symptoms in later life.Publication Social Networks and HIV/AIDS Risk Perceptions(2007-02-01) KOHLER, HANS-PETER; Behrman, Jere R; Watkins, Susan CottsUnderstanding the determinants of individuals' perceptions of their risk of becoming infected with HIV and their perceptions of acceptable strategies of prevention is an essential step toward curtailing the spread of this disease. We focus in this article on learning and decision-making about AIDS in the context of high uncertainty about the disease and appropriate behavioral responses. We argue that social interactions are important for both. Using longitudinal survey data from rural Kenya and Malawi, we test this hypothesis. We investigate whether social interactions—and especially the extent to which social network partners perceive themselves to be at risk—exert causal influences on respondents' risk perceptions and on one approach to prevention, spousal communication about the threat of AIDS to the couple and their children. The study explicitly allows for the possibility that important characteristics, such as unobserved preferences or community characteristics, determine not only the outcomes of interest but also the size and composition of networks. The most important empirical result is that social networks have significant and substantial effects on risk perceptions and the adoption of new behaviors even after we control for unobserved factors.Publication Using Anthropometric Indicators for Mexicans in the United States and Mexico to Understand the Selection of Migrants and the "Hispanic Paradox"(2005-09-01) Soldo, Beth J; Crimmins, Eileen M; Alley, Dawn; Kim, Jung KiAnthropometric measures including height provide an indication of childhood health that allows exploration of relationships between early life circumstances and adult health. Height can also be used to provide some indication of how early life health is related to selection of migrants and the Hispanic paradox in the United States. This article joins information on persons of Mexican nativity ages 50 and older in the United States collected in the National Health and Nutrition Examination Survey IV (NHANES IV 1999-2002) with a national sample of persons of the same age living in Mexico from the Mexican Health and Aging Survey (MHAS 2001) to examine relationships between height, education, migration, and late-life health. Mexican immigrants to the United States are selected for greater height and a high school, rather than higher or lower, education. Return migrants from the United States to Mexico are shorter than those who stay. Height is related to a number of indicators of adult health. Results support a role for selection in the Hispanic paradox and demonstrate the importance of education and childhood health as determinants of late-life health in both Mexico and the United States.