Dalton Conley

Is biology destiny ? Birth weight and life chances

Two key questions are addressed regarding the intersection of socioeconomic status biology and low birth weight over the life course. First do the income and other socioeconomic conditions of a mother during her pregnancy affect her chances of having a low-birth-weight infant net of her own birth weight that of the father and other family-related unobserved factors? Second does an individuals birth weight status affect his or her adult life chances net of socioeconomic status? These questions have implications for the way the authors conceive of the relationship between socioeconomic status and health over the life course specifically in sorting out causal directionality. The authors use intergenerational data from the Panel Study of Income Dynamics for the years 1968 through 1992. Results of sibling comparisons (family-fixed-effects models) demonstrate that maternal income does not appear to have a significant impact on birth weight. However low birth weight results in lower educational attainment net of other factors. These findings suggest that when considered across generations causality may not be as straightforward as implied by cross-sectional or unigenerational longitudinal studies. (authors)

Common genetic variants associated with cognitive performance identified using the proxy-phenotype method

Significance We identify several common genetic variants associated with cognitive performance using a two-stage approach: we conduct a genome-wide association study of educational attainment to generate a set of candidates, and then we estimate the association of these variants with cognitive performance. In older Americans, we find that these variants are jointly associated with cognitive health. Bioinformatics analyses implicate a set of genes that is associated with a particular neurotransmitter pathway involved in synaptic plasticity, the main cellular mechanism for learning and memory. In addition to the substantive contribution, this work also serves to show a proxy-phenotype approach to discovering common genetic variants that is likely to be useful for many phenotypes of interest to social scientists (such as personality traits). We identify common genetic variants associated with cognitive performance using a two-stage approach, which we call the proxy-phenotype method. First, we conduct a genome-wide association study of educational attainment in a large sample (n = 106,736), which produces a set of 69 education-associated SNPs. Second, using independent samples (n = 24,189), we measure the association of these education-associated SNPs with cognitive performance. Three SNPs (rs1487441, rs7923609, and rs2721173) are significantly associated with cognitive performance after correction for multiple hypothesis testing. In an independent sample of older Americans (n = 8,652), we also show that a polygenic score derived from the education-associated SNPs is associated with memory and absence of dementia. Convergent evidence from a set of bioinformatics analyses implicates four specific genes (KNCMA1, NRXN1, POU2F3, and SCRT). All of these genes are associated with a particular neurotransmitter pathway involved in synaptic plasticity, the main cellular mechanism for learning and memory.

Black–White Achievement Gap and Family Wealth

This article examines the extent to which family wealth affects the Black-White test score gap for young children based on data from the Panel Study of Income Dynamics (aged 3-12). This study found little evidence that wealth mediated the Black-White test scores gaps, which were eliminated when child and family demographic covariates were held constant. However, family wealth had a stronger association with cognitive achievement of school-aged children than that of preschoolers and a stronger association with school-aged childrens math than on their reading scores. Liquid assets, particularly holdings in stocks or mutual funds, were positively associated with school-aged childrens test scores. Family wealth was associated with a higher quality home environment, better parenting behavior, and childrens private school attendance.

Welfare state and infant mortality.

This article seeks to understand the effects of welfare‐state spending on infant mortality rates. Infant mortality was chosen for its importance as a social indicator and its putative sensitivity to state action over a short time span. Country fixed‐effects models are used to determine that public health spending does have a significant impact in lowering infant mortality rates, net of other factors, such as economic development, and that this effect is cumulative over a five‐year time span. A net effect of health spending is also found, even when controlling for the level of spending in the year after which the outcome is measured (to account for spurious effects or reverse causation). State spending affects infant mortality both through social mechanisms and through medical ones. This article also shows that the impact of state spending may vary by the institutional structure of the welfare state. Finally, this study tests for structural breaks in the relationship between health spending and infant mortality and finds none over this time period.

Gender, Body Mass, and Socioeconomic Status: New Evidence from the PSID

Previous research provides evidence of a negative effect of body mass on womens economic outcomes. We extend this research by using a much older sample of individuals from the Panel Study of Income Dynamics and by using a body mass measure that is lagged by 15 years instead of the traditional 7 years. One of the main contributions of this paper is a replication of previous research findings given our differing samples and measures. We compare OLS estimates with sibling fixed effects estimates and find that obesity is associated with an 18% reduction in womens wages, a 25% reduction in womens family income, and a 16% reduction in womens probability of marriage. These effects are robust--they persist much longer than previously understood and they persist across the life course, affecting older women as well as younger women.

Birth weight and income: interactions across generations.

This paper attempts to answer a series of questions regarding the interaction of income and birth weight across generations. First, does the effect of the income of a mother during her pregnancy on her infants birth weight depend on the familys birth weight history (genetic predisposition)? Second, does the effect of low birth weight status on adult life chances depend on income during early childhood? These questions have implications for the way we envision the biological and social worlds as interacting across generations. To address these issues, this study uses intergenerational data from the Panel Study of Income Dynamics, survey years 1968 through 1992. Results of sibling comparisons (family-fixed-effects models) demonstrate that maternal income has a significant impact on birth weight for those infants who are already at high risk hereditarily (i.e., who have a low birth weight parent). However, it is not clear whether income acts as a developmental buffer for low birth weight infants as their lives progress. These findings suggest the existence of biosocial interactions between hereditary predisposition and socio-economic environment.

A Room With a View or a Room of One's Own? Housing and Social Stratification

This study attempts to understand the role that housing plays in the system of social stratification. First, it generates a model of how housing outcomes are stratified along dimensions of socioeconomic status and race. Second, it asks what role housing conditions play in the system of educational stratification of offspring. Using two-generational data from the Panel Study of Income Dynamics, this paper demonstrates that home ownership is predicted by family income and race and that this indicator has a significant effect in predicting the educational attainment of offspring. Household crowding is also related to income and race and also affects the educational attainment of offspring. Meanwhile, housing quality—as measured by the physical condition of the unit—is not related to income or race and has no effect on educational attainment. Of particular note is that when socioeconomic status and housing conditions are held constant, African-Americans demonstrate more than a half-grade advantage over their non-black counterparts in years of completed schooling. In conclusion, the paper argues that housing matters not only for the immediate well-being of families, but also for the life-chances of the subsequent generation, and should be a standard variable in the conception of class background.

Genetic and educational assortative mating among US adults

Significance It is well established that individuals are more similar to their spouses than other individuals on important traits, such as education level. The genetic similarity, or lack thereof, between spouses is less well understood. We estimate the genome-wide genetic similarity of spouses and compare the magnitude of this value to a comparable measure of educational similarity. We find that spouses are more genetically similar than two individuals chosen at random but this similarity is at most one-third the magnitude of educational similarity. Furthermore, social sorting processes in the marriage market are largely independent of genetic dynamics of sexual selection. Understanding the social and biological mechanisms that lead to homogamy (similar individuals marrying one another) has been a long-standing issue across many fields of scientific inquiry. Using a nationally representative sample of non-Hispanic white US adults from the Health and Retirement Study and information from 1.7 million single-nucleotide polymorphisms, we compare genetic similarity among married couples to noncoupled pairs in the population. We provide evidence for genetic assortative mating in this population but the strength of this association is substantially smaller than the strength of educational assortative mating in the same sample. Furthermore, genetic similarity explains at most 10% of the assortative mating by education levels. Results are replicated using comparable data from the Framingham Heart Study.

Heritability and the Equal Environments Assumption: Evidence from Multiple Samples of Misclassified Twins

Classically derived estimates of heritability from twin models have been plagued by the possibility of genetic-environmental covariance. Survey questions that attempt to measure directly the extent to which more genetically similar kin (such as monozygotic twins) also share more similar environmental conditions represent poor attempts to gauge a complex underlying phenomenon of GE-covariance. The present study exploits a natural experiment to address this issue: Self-misperception of twin zygosity in the National Longitudinal Survey of Adolescent Health (Add Health). Such twins were reared under one “environmental regime of similarity” while genetically belonging to another group, reversing the typical GE-covariance and allowing bounded estimates of heritability for a range of outcomes. In addition, we examine twins who were initially misclassified by survey assignment—a stricter standard—in three datasets: Add Health, the Minnesota Twin Family Study and the Child and Adolescent Twin Study in Sweden. Results are similar across approaches and datasets and largely support the validity of the equal environments assumption.

The Promise and Challenges of Incorporating Genetic Data into Longitudinal Social Science Surveys and Research

In this paper, I argue that social science and genomics can be integrated; however, the way this marriage is currently occurring rests on spurious methods and assumptions and, as a result, will yield few lasting insights. However, recent advances in both econometrics and in developmental genomics provide scientists with a novel opportunity to understand how genes and environment interact to produce social outcomes. Key to any causal inference about the interplay between genes and social environment is that either genotype be exogenously manipulated (i.e. through sibling fixed effects) while environmental conditions are held constant, and/or that environmental variation is exogenous in nature, i.e. experimental or arising from a natural experiment of sorts. Further, initial allele selection should be motivated by findings from genetic experiments in model animal studies linked to orthologous human genes. Likewise, genetic associations found in human population studies should then be tested through knock-out and over-expression studies in model organisms.