Social Science Methods for Twins Data: Integrating Causality, Endowments, and Heritability

Abstract

Twins have been extensively used in economics, sociology and behavioral genetics to investigate the role of genetic endowments on a broad range of social, demographic and economic outcomes. However, the focus in these literatures has been distinct: the economic literature has been primarily concerned with the need to control for unobserved endowments—including as an important subset, genetic endowments—in analyses that attempt to establish the impact of one variable, often schooling, on a variety of economic, demographic and health outcomes. Behavioral genetic analyses have mostly been concerned with decomposing the variation in the outcomes of interest into genetic, shared environmental and non-shared environmental components, with recent multivariate analyses investigating the contributions of genes and the environment to the correlation and causation between variables. Despite the fact that twins studies and the recognition of the role of endowments are central to both of these literatures, they have mostly evolved independently. In this paper we develop formally the relationship between the economic and behavioral genetic approaches to the analyses of twins, and we develop an integrative approach that combines the identification of causal effects, which dominates the economic literature, with the decomposition of variances and covariances into genetic and environmental factors that is the primary goal of behavioral genetic approaches. We apply this integrative ACE-β approach to an illustrative investigation of the impact of schooling on several demographic outcomes such as fertility and nuptiality and health.

Employment sector and pay gaps: Genetic and environmental influences

“…The latest literature also attempts to integrate the economic and behavioural genetics approaches in the analysis of twins (e.g., Kohler et al 2010). Following Miller et al (1996), I…”

Are genetic markers of interest for economic research?

“…7 More recent research has shifted from using data collected in traditional surveys to using data from either incentivized experiments or surveys, to explore the heritability in different measures of economic preferences (e.g., Wallace et al 2007;Cesarini et al 2008Cesarini et al , 2009Cesarini et al , 2010Cesarini et al , 2012. See Kohler et al (2011) for a discussion of how to leverage twin studies to model unobserved genetic endowments and causal pathways. Last, we discuss genome-wide complex trait analysis (GCTA) a method that uses restricted maximum likelihood estimation to estimate heritability from molecular genetic data in the section on gene by environment interactions.…”

The Biodemography of Fertility: A Review and Future Research Frontiers

“…This approach combines insights from econometrics and behavioural genetics by integrating the MZ-fixed effects approach as a direct link between phenotypes into the structural equation model. It therefore potentially identifies a causal link between two traits additional to genetic and environmental endowment-particularly if a valid instrumental variable can be found (these and related approaches are detailed in Kohler et al 2011). More importantly, in the realm of molecular genetics, actual genetic data is being collected as well as further development of statistical tools (Yang et al 2010(Yang et al , 2011.…”

“…If the genetic correlation is 0 the genetically based variance between trait 1 and 2 are independent. For a more detailed empirical explanation, refer to Kohler et al (2011).…”

“…Several studies engage in more complex (twin) modelling (e.g., Kohler et al 2011) estimating, for example, bivariate genetic models. Following the same logic as in classic twin studies, it is possible to estimate the extent to which the same genetic and environmental factors are important for two different traits.…”