Does Education Mediate the Relationship Between Iq and Age of First Birth? A Behavioural Genetic Analysis

Abstract

This study presents a multivariate behavioural genetic analysis of the relationship between education, intelligence and age of first birth. Analyses investigated the mediational role of education in explaining the relationship between intelligence and age of first birth at both the phenotypic and behavioural genetic level. The data come from the National Longitudinal Survey of Youth (NLSY), a nationally representative survey that included genetically informative full-and half-sibling pairs (n=1423 pairs). Respondents were aged 14 to 22 when contacted in 1979. Heritability estimates were 0·32, 0·50 and 0·06 for IQ, education and age of first birth, respectively. Shared environment estimates were 0·35, 0·23 and 0·20 respectively. Common genetic and shared environmental factors were substantial in explaining the relationship between intelligence and education, and also education and age of first birth. Education partially mediated the relationship between intelligence and age of first birth only in the phenotypic analyses. After considering the genetic and shared environmental factors that influence all three variables, evidence for mediation was less convincing. This pattern of results suggests that the apparent mediational role of education at the phenotypic level is in fact the result of underlying genetic and shared environmental influences that affect education, IQ and age of first birth in common.

Education and Cognitive Ability as Direct, Mediating, or Spurious Influences on Female Age at First Birth: Behavior Genetic Models Fit to Danish Twin Data

“…1), the original coefficient of b COG→AFB = .08 went to 0, b COG→ED = .66, and b ED→AFB = .31. We note that these results are very similar to those from the Neiss et al (2002) study from the United States. MacKinnon, Lockwood, and Williams (2004) provide statistical tests and confidence intervals to test whether b COG→AFB is still significant after introducing a mediator, although there is no point in testing whether a sample coefficient of zero is different from a population parameter of zero.…”

“…Rowe, Vesterdal, and Rodgers (1999) used National Longitudinal Survey of Youth (NLSY) data to model income and found the same pattern as Retherford and Sewell (1989): education was a more direct (and likely causal) antecedent for differences in income than intelligence. Neiss, Rowe, and Rodgers (2002) replicated Retherford and Sewell's (1989) results using the same variables in the NLSY. They defined a model in which IQ and education were used as predictors of AFB.…”

“…In addition to the results in figure 3, we also present statistics from this analysis in table 3, which presents the univariate heritabilities (h 2 ) and shared environmental variance (c 2 ) estimated for each of our primary variables (and we add the Neiss et al [2002] results to show the similarity). AFB had no univariate heritability, so it had no genetic variance to overlap that of cognitive ability or education in figure 4 (and note the absence of patterned correlations or covariances in relation to genetic category in table 2).…”

Multivariate Cholesky Models of Human Female Fertility Patterns in the NLSY

“…A small amount of previous research has been done to identify and model such processes; in addition to the Kohler and Rodgers (2003) work that considered the interaction between education and fertility, Neiss et al (2002) developed models of the interaction between education, income, and age-at-first-childbearing. Further development of such gene-gene and gene-environment interaction models would appear to show great promise for future research attempting to understand genetic and environmental influences on fertility.…”

Smoking during pregnancy and offspring externalizing problems: An exploration of genetic and environmental confounds

“…Third, we have evidence of concurrent validity by using findings based on these kinship links and comparing them to those from other studies. For example, compare results on age-at-first-intercourse from Rodgers, Rowe, and Buster, (1999), to the molecular genetic results from Miller et al, (1999); compare Rodgers, Buster, & Rowe's (2001) delinquency patterns to those in Miles and Carey (1997); or compare the multivariate patterns across education and IQ in Neiss, Rowe, and Rodgers (2002) to those from Tambs et al, (1989).…”