Cohort Studies

April 17-18, 2015
Dora Costa, University of California, Los Angeles and Robert Pollak, Washington University in St. Louis, Organizers

Daniel W. Belsky, Avshalom Caspi, and Terrie Moffitt, Duke University, Duke University, and Richie Poulton, University of Otago

Quantification of Biological Aging in Young Adults

Aging is the leading cause of chronic diseases associated with disability and early death. New research suggests the possibility that aging can be slowed. Most human studies of aging focus on older individuals, many of whom already have chronic disease. Here, Belsky, Caspi, Poulton, and Moffitt study aging in young, healthy humans up to age 38 in the Dunedin Study. The researchers show that young individuals of the same chronological age can vary in their "biological age" (measured age-related decline in physiological integrity of multiple organ systems). As compared to same-chronological-age peers, biologically older individuals were less physically able, showed evidence of cognitive decline and brain aging, perceived themselves to be in worse health, and looked older. Faster biological aging in the first half of the life course was predicted by genetic risk for age-related disease. Measures of biological age can be used to identify causes of aging and to evaluate rejuvenation-therapies.

Chulhee Lee and Esther Lee, Seoul National University

Son Preference, Sex-Selective Abortion, and Parental Investment in Girls in Korea: Evidence from the Year of the White Horse

Lee and Lee investigate how the selection of offspring gender in the presence of son preference affects the parental investments in girls and boys in South Korea. To identify the magnitude of parental son preference, the researchers exploit two types of variations in the extent of sex selections, namely, (1) the provincial variations in the sex ratio at birth that result from regional differences in cultural norms and religious beliefs, and (2) the temporary increase in the sex ratio at birth in 1990 (the year of the White Horse), which has been driven by zodiacal preference. The authors conduct triple difference estimations to examine how the gender differences in parental investment in the health and education of children change across regions and cohorts. They find that the relative parental investments in girls in the form of breast feeding and private out-of-school education are significantly larger for cohorts born in 1990 and that the effect of the year of the White Horse is more strongly observed in regions with higher sex ratios at birth. A higher prevalence of sex-selective abortions led to greater parental investments in girls than in boys. The rise of sex-selective abortions in Korea from the early 1980s to the early 2000s unintendedly improved the human capital development of females who were selectively born to parents with weaker bias against daughters.

Sarah Miller, University of Michigan, and Laura R. Wherry, University of California, Los Angeles

The Long-Term Health Effects of Early Life Medicaid Coverage

Although the link between the fetal environment and later life health and achievement is well-established, few studies have evaluated the extent to which public policies aimed at improving fetal health can generate benefits that persist into adulthood. In this study, Miller and Wherry evaluate how a rapid expansion of prenatal and child health insurance through the Medicaid program affected the adult health and health care utilization of individuals born between 1979 and 1993 who gained access to coverage in utero and as children. The researchers find that those whose mothers gained eligibility for prenatal coverage under Medicaid have lower rates of obesity as adults, with suggestive evidence of lower body mass indices and lower incidence of chronic illnesses. Using administrative data on hospital discharges, the authors find that cohorts who gained in utero Medicaid eligibility have fewer hospitalizations related to endocrine, nutritional and metabolic diseases, and immunity disorders as adults, with particularly pronounced reductions in visits associated with diabetes and obesity. The researchers find effects of public eligibility in other periods of childhood on hospitalizations later in life, but these effects are small. The results indicate that expanding Medicaid prenatal coverage had long-term benefits for the health of the next generation.

Amanda E. Kowalski, Yale University and NBER

What Do Longitudinal Data on Millions of Hospital Visits Tell us about the Value of Public Health Insurance as a Safety Net for the Young and Privately Insured?

Young people with private health insurance sometimes transition to the public health insurance safety net after they get sick, but popular sources of cross-sectional data obscure how frequently these transitions occur. Kowalski uses longitudinal data on almost all hospital visits in New York from 1995 to 2011. The researcher shows that young privately insured individuals with diagnoses that require more hospital visits in subsequent years are more likely to transition to public insurance. Ignoring the longitudinal transitions in the data, Kowalski obscures over 80% of the value of public health insurance to the young and privately insured.

Achyuta Adhvaryu, University of Michigan; Steven A. Bednar, Elon University; Teresa Molina and Anant Nyshadham, University of Southern California; and Quynh T. Nguyen, World Bank

Salt Iodization and the Enfranchisement of the American Worker

In 1924, The Morton Salt Company began nationwide distribution of iodine-fortified salt. Access to iodine, a key determinant of cognitive ability, rose sharply. Adhvaryu, Bednar, Molina, Nguyen, and Nyshadham compare outcomes for cohorts exposed in utero to iodized salt with those of slightly older, unexposed cohorts, across states with high versus low iodine deficiency rates prior to salt fortification. Labor force participation rose by 0.6 percentage points, driven by a rise in low-skill employment. Educational attainment declined by 0.09 years, mainly due to decreased primary school completion, consistent with the hypothesis that cognitive ability and schooling are substitutes at low levels of schooling.

Alissa Goodman and Heather Joshi, University of London, and Bilal Nasim, Institute of Education

Social and Emotional Skills in Childhood and Their Long-Term Effects on Adult Life

In this report Goodman, Joshi, Nasim, and Tyler assess the evidence on the long-run associations between social and emotional skills in childhood and adult outcomes. The researchers report findings from an extensive literature review, and from their own new research. There are three key elements: (i) A literature review of evidence relating to the relationship between social and emotional skills in childhood and adult outcomes; (ii) New analysis of the British Cohort Study about these relationships across a wide range of outcomes, including a particular focus on the role of social and emotional skills in transmitting 'top job' status between parents and their children; (iii) New, preliminary analysis of how the gaps in some of the skills assessed in (ii) are emerging in children in the U.K. born around the millennium.

Eric Schneider, University of Sussex

Fetal Health Stagnation: Have Health Conditions in Utero Improved in the US and Western and Northern Europe over the past 150 Years?

Between 1850 and the present many standard indicators of human health have improved dramatically around the world. Crude death, child mortality, infant mortality and stillbirth rates have fallen. Life expectancy and average adult height have increased. Given the tremendous improvement in human health over the past 150 years, one might assume that conditions for children in utero were also improving. However, there has not been a systematic study of multiple fetal health indicators to determine whether this was true. In this paper, Schneider presents such an analysis. Examining several proxies for fetal health including birth weights, stillbirth rates and early neonatal mortality rates, he argues that there has been little change in fetal health conditions from the mid-nineteenth century to the present in North America and Western and Northern Europe.

Gabriella Conti, University College London; James J. Heckman, University of Chicago; NBER; American Bar Foundation; Institute for the Study of Labor (IZA); CESifo (Center for Economic Studies and Ifo Institute); and Rodrigo R. Pinto Sr., University of Chicago

The Health Effects of Two Influential Early Childhood Interventions

A growing literature establishes that high-quality early childhood interventions that enrich the environments of disadvantaged children have substantial long-run impacts on a variety of social and economic outcomes. Much less is known about their effects on health. This paper examines the long-term health impacts of two of the oldest and most widely cited U.S. early childhood interventions evaluated by the method of randomization with long term follow-up: the Perry Preschool Project (PPP) and the Abecedarian Project (ABC). Conti, Heckman, and Pinto document that the boys randomly assigned to the treatment group of the PPP have significantly lower prevalence of behavioral risk factors in adulthood compared to those randomized to the control condition, while those who received the ABC intervention enjoy better physical health. Estimated effects are much weaker for girls. The researchers' permutation-based inference procedure accounts for the small sample sizes of the ABC and PPP interventions, for the multiplicity of the hypotheses tested, and for non-random attrition from the panel follow-ups. The authors conduct a dynamic mediation analysis to shed light on the mechanisms producing the estimated treatment effects. They document a significant role played by enhanced childhood traits, above and beyond experimentally enhanced adult socioeconomic status. Overall, the researchers' results show the potential of early life interventions for preventing disease and promoting health.

Jesse Anttila-Hughes and Thomas Dreesen, University of San Francisco

Heterogeneous Long-Term Human Capital Impacts of Climate Variability in Rural and Urban Bangladesh

The increase in climatic variability that is expected to occur due to climate change poses a particular risk for the developing world, where reliance on rain-fed agriculture and exposure to weather-driven hazards are both common. In this paper, Anttila-Hughes and Dreesen combine survey data on adult Bangladeshi women with historical climate data to provide evidence that these competing effects make the relationship between climate variability around time of birth and latter-life human capital fundamentally different in rural versus urban areas. The researchers find that rains in rural areas positively predict adult cognitive outcomes when experienced in-utero, and height when experienced during infancy, broadly consistent with findings in health economics and human developmental biology. In urban areas the authors find that the timing of effects is similar but the impacts are negative. They document research from agronomy, ecology, and public health that suggests that this urban-rural divide is driven by rains causing improved agricultural yields in rural areas but worsened sanitation in urban ones, and find support for the sanitation hypothesis by using children's data to demonstrate that rainfall at time of survey predicts wasting in urban areas only. Together, the results imply that the long-term welfare impacts of climate variability are strongly conditioned by the local environment, and that urbanization in developing countries may less reduce vulnerability to climate change than simply altering its nature.

Dave Donaldson, Stanford University and NBER, and Daniel Keniston, Yale University and NBER

How Positive Was the Positive Check? Investment and Fertility in the Aftermath of the 1918 Influenza in India

Aryeh Stein, Emory University

Child Growth and Human Capital: Data from COHORTS

In this paper, Stein reviews recent findings from the COHORTS collaborative, a project that pools data from the five birth cohort studies in low- and middle-income countries that have reached adulthood. The cohorts include people born in Pelotas, Brazil; Guatemala; New Delhi, India; Cebu, the Philippines; and Soweto-Johannesburg, South Africa. Through the use of regression residuals, Stein has addressed problems caused by the linear dependence of repeated measures of size. He finds that important human capital outcomes in adulthood (height, body mass index, schooling attainment, systolic blood pressure, plasma glucose) have differential associations with height change and relative weight change in selected periods of growth. The implications for interventions to improve child growth in low and model income countries are discussed.

Joanna Lahey, Texas A&M University and NBER, and Douglas Oxley, University of Wyoming

Discrimination at the Intersection of Age, Race, and Gender: Evidence from a Lab-in-the-field Experiment

Although hiring discrimination has been found in many audit studies and laboratory experiments, little is known about how, why, and for whom this discrimination occurs. This paper combines the new technologies of resume randomization and eye-tracking within a laboratory setting to get a clearer picture of the mechanics of discrimination. Lahey and Oxley found strong evidence of (quadratic) age discrimination based on date of high school graduation as well as evidence for race discrimination based on names. The authors did not find direct evidence of gender discrimination, but gender interacts with race and age. Results on race*age are particularly striking, with resumes with black names rated at a lower level for younger ages but eventually becoming preferred over resumes with white names as the age on the resume increases, while white resumes show the opposite pattern. Participants also spent longer times looking at young resumes compared to older resumes, and longer looking at white resumes compared to black resumes. Patterns of what helps or hurts a resume vary by age and by race. The amount of time spent looking at different parts of the resume also varies by age and race, providing evidence of implicit biases.

Avron Spiro, Boston University

Long-Term Psychological Outcomes of Military Experience

Hans Henrik Sievertsen and Miriam Wüst, The Danish National Centre for Social Research

Discharge on the Day of Birth, Parental Response and Health and Schooling Outcomes

Exploiting the Danish roll-out of same-day discharge policies, Sievertsen and Wüst find that treated newborns have a higher probability of first-month hospital readmission. This result may suggest that parents substitute postpartum hospital stays with readmissions. However, a same-day discharge also increases the number of mother and child general practitioner contacts in the first three years and decreases children's ninth grade GPA. Longer-run effects are strongest for at-risk children. Complementing the analyses of administrative data with survey data, the researchers show that a same-day discharge impacts health and schooling in the longer run through both its effects on children's health and on parental investments.

Adam Isen, Department of the Treasury; Maya Rossin-Slater, University of California, Santa Barbara, and Reed Walker, University of California, Berkeley and NBER

Heat and Long-Run Human Capital Formation

Isen, Rossin-Slater, and Walker study how exposure to extreme temperatures in early periods of child development affects adult labor market outcomes. The researchers' analysis uses administrative earnings records for over 12 million individuals born between 1969 and 1977 linked to fine-scale daily weather data. The authors calculate the length of time each individual is exposed to different temperatures during the in utero and early childhood periods, and they estimate flexible models that allow for non-linearities in the relationship between temperature and later life outcomes. The researchers find that an extra day with mean temperatures above 32C (89.6F) in utero and in the first year of life is associated with a 0.2 percent reduction in annual earnings between the ages of 29 and 31. This effect is evident in multiple periods of child development, ranging from the first trimester of gestation to age 6-12 months. Lastly, household air conditioning adoption, which increased dramatically over the time period studied, mitigates nearly all of the estimated temperature sensitivity.

Govert Bijwaard, NIDI, and Lambert Lumey, Columbia University

Effects of Prenatal Famine on Conscript Heights at Age 18

Family studies suggest that most of the variation in height is under genetic control but environmental factors are clearly important as shown by the continuing secular increase in heights across the world. To date, most attention has been paid to material conditions after birth. There is an increasing interest however on the long term effects of living conditions before birth. Bijwaard and Lumey therefore examined these effects in the setting of the Dutch famine of 1944-45 at the end of WWII. The researchers used military examination records of 371,000 surviving men born from 1944-47 in the Netherlands to analyze conscript heights by place and date of birth. Conscripts born in the north were taller than average (177.9 cm) and conscripts from the south shorter (175.3 cm). Applying difference-in-difference methods to evaluate conscript heights by birth region and date of birth in relation to famine, the researchers find by OLS regression that conscripts exposed to the famine in early gestation were 0.6 cm taller than expected. They also find that the number of conscripts born in the famine cities was 50% lower than expected in comparison with numbers in non-famine years. The authorsÂ’ findings of increased conscript heights after prenatal famine exposure early in gestation are unexpected. As the number of conscripts in this group is much smaller than normal, the findings point towards the over-representation of the most privileged and healthiest mothers and their children in this group as a possible explanation.

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