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Equality in Educational Policy and the Heritability of Educational Attainment.

Colodro-Conde L, Rijsdijk F, Tornero-Gómez MJ, Sánchez-Romera JF, Ordoñana JR - PLoS ONE (2015)

Bottom Line: The action of effect is hypothesized to be a decrease of shared environmental (e.g., family socioeconomic status or parents' education) influences on educational attainment, giving more room for genetic differences between individuals to impact on the variation of the trait.However, this hypothesis has not yet found consistent evidence.Our results support the role of educational policy in affecting the relative weight of genetic and environmental factors on educational attainment, such that increasing equality in educational opportunities increases heritability estimates by reducing variation of non-genetic familial origin.

View Article: PubMed Central - PubMed

Affiliation: Murcia Twin Registry, Department of Human Anatomy and Psychobiology, University of Murcia, & IMIB-Arrixaca, Murcia, Spain.

ABSTRACT
Secular variation in the heritability of educational attainment are proposed to be due to the implementation of more egalitarian educational policies leading to increased equality in educational opportunities in the second part of the 20th century. The action of effect is hypothesized to be a decrease of shared environmental (e.g., family socioeconomic status or parents' education) influences on educational attainment, giving more room for genetic differences between individuals to impact on the variation of the trait. However, this hypothesis has not yet found consistent evidence. Support for this effect relies mainly on comparisons between countries adopting different educational systems or between different time periods within a country reflecting changes in general policy. Using a population-based sample of 1271 pairs of adult twins, we analyzed the effect of the introduction of a specific educational policy in Spain in 1970. The shared-environmental variance decreased, leading to an increase in heritability in the post-reform cohort (44 vs. 67%) for males. Unstandardized estimates of genetic variance were of a similar magnitude (.56 vs. .57) between cohorts, while shared environmental variance decreased from .56 to .04. Heritability remained in the same range for women (40 vs. 34%). Our results support the role of educational policy in affecting the relative weight of genetic and environmental factors on educational attainment, such that increasing equality in educational opportunities increases heritability estimates by reducing variation of non-genetic familial origin.

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Related in: MedlinePlus

Path diagram for the basic univariate twin model used estimation of sources of variance in EA.The additive genetic factors (A) have a correlation of 1 between MZ twins and 0.5 between DZ twins, respectively. Shared family environment (C) is correlated 1 for both MZ and DZ twins. Unique environment (E) is the source of variance that will result in differences among members of one family and is, thus, uncorrelated between members of MZ and DZ pairs. The regression coefficients for A, C and E effects, are ‘a’, ‘c’ and ‘e’, respectively.
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pone.0143796.g002: Path diagram for the basic univariate twin model used estimation of sources of variance in EA.The additive genetic factors (A) have a correlation of 1 between MZ twins and 0.5 between DZ twins, respectively. Shared family environment (C) is correlated 1 for both MZ and DZ twins. Unique environment (E) is the source of variance that will result in differences among members of one family and is, thus, uncorrelated between members of MZ and DZ pairs. The regression coefficients for A, C and E effects, are ‘a’, ‘c’ and ‘e’, respectively.

Mentions: The data were analysed using Structural Equation Modelling (SEM), which allows one to test specific theoretical models in a multiple group approach. We applied the classical twin design [27, 28] to estimate the contribution of genetic and environmental factors to population variation in EA, using the statistical software package Mx [29]. Basically, the classical twin model compares intra-pair twin resemblance (twin correlations) between monozygotic (MZ) and dizygotic (DZ) twin pairs. The expectation of this difference forms the basis for estimating the contribution of latent variables defined as additive genetic factors (i.e. the sum of allelic effects across multiple genes) (A); common environment (i.e. environmental influences which make them similar, such as parental characteristics, intrauterine conditions, or family socioeconomic status) (C); and unique environmental factors (i.e. idiosyncratic experiences, as well as measurement error) (E). MZ twins share 100% of their segregating genes, while DZ share, on average, 50%. Hence the MZ correlation depends on their genetic makeup plus the effect of shared environmental factors (rMZ = A + C), while the DZ correlation is due to sharing half the genetic effects plus shared environmental factors (rDZ = ½ A + C). If MZ twins resemble each other significantly more than DZ twins, that is an indication of genetic effects on individual differences in a given trait. If DZ twins resemble each other more than half the resemblance of MZ twins, that is an indication of shared environmental effects. Non-shared environmental factors (E) are uncorrelated across individuals, and include measurement error (Fig 2).


Equality in Educational Policy and the Heritability of Educational Attainment.

Colodro-Conde L, Rijsdijk F, Tornero-Gómez MJ, Sánchez-Romera JF, Ordoñana JR - PLoS ONE (2015)

Path diagram for the basic univariate twin model used estimation of sources of variance in EA.The additive genetic factors (A) have a correlation of 1 between MZ twins and 0.5 between DZ twins, respectively. Shared family environment (C) is correlated 1 for both MZ and DZ twins. Unique environment (E) is the source of variance that will result in differences among members of one family and is, thus, uncorrelated between members of MZ and DZ pairs. The regression coefficients for A, C and E effects, are ‘a’, ‘c’ and ‘e’, respectively.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4664401&req=5

pone.0143796.g002: Path diagram for the basic univariate twin model used estimation of sources of variance in EA.The additive genetic factors (A) have a correlation of 1 between MZ twins and 0.5 between DZ twins, respectively. Shared family environment (C) is correlated 1 for both MZ and DZ twins. Unique environment (E) is the source of variance that will result in differences among members of one family and is, thus, uncorrelated between members of MZ and DZ pairs. The regression coefficients for A, C and E effects, are ‘a’, ‘c’ and ‘e’, respectively.
Mentions: The data were analysed using Structural Equation Modelling (SEM), which allows one to test specific theoretical models in a multiple group approach. We applied the classical twin design [27, 28] to estimate the contribution of genetic and environmental factors to population variation in EA, using the statistical software package Mx [29]. Basically, the classical twin model compares intra-pair twin resemblance (twin correlations) between monozygotic (MZ) and dizygotic (DZ) twin pairs. The expectation of this difference forms the basis for estimating the contribution of latent variables defined as additive genetic factors (i.e. the sum of allelic effects across multiple genes) (A); common environment (i.e. environmental influences which make them similar, such as parental characteristics, intrauterine conditions, or family socioeconomic status) (C); and unique environmental factors (i.e. idiosyncratic experiences, as well as measurement error) (E). MZ twins share 100% of their segregating genes, while DZ share, on average, 50%. Hence the MZ correlation depends on their genetic makeup plus the effect of shared environmental factors (rMZ = A + C), while the DZ correlation is due to sharing half the genetic effects plus shared environmental factors (rDZ = ½ A + C). If MZ twins resemble each other significantly more than DZ twins, that is an indication of genetic effects on individual differences in a given trait. If DZ twins resemble each other more than half the resemblance of MZ twins, that is an indication of shared environmental effects. Non-shared environmental factors (E) are uncorrelated across individuals, and include measurement error (Fig 2).

Bottom Line: The action of effect is hypothesized to be a decrease of shared environmental (e.g., family socioeconomic status or parents' education) influences on educational attainment, giving more room for genetic differences between individuals to impact on the variation of the trait.However, this hypothesis has not yet found consistent evidence.Our results support the role of educational policy in affecting the relative weight of genetic and environmental factors on educational attainment, such that increasing equality in educational opportunities increases heritability estimates by reducing variation of non-genetic familial origin.

View Article: PubMed Central - PubMed

Affiliation: Murcia Twin Registry, Department of Human Anatomy and Psychobiology, University of Murcia, & IMIB-Arrixaca, Murcia, Spain.

ABSTRACT
Secular variation in the heritability of educational attainment are proposed to be due to the implementation of more egalitarian educational policies leading to increased equality in educational opportunities in the second part of the 20th century. The action of effect is hypothesized to be a decrease of shared environmental (e.g., family socioeconomic status or parents' education) influences on educational attainment, giving more room for genetic differences between individuals to impact on the variation of the trait. However, this hypothesis has not yet found consistent evidence. Support for this effect relies mainly on comparisons between countries adopting different educational systems or between different time periods within a country reflecting changes in general policy. Using a population-based sample of 1271 pairs of adult twins, we analyzed the effect of the introduction of a specific educational policy in Spain in 1970. The shared-environmental variance decreased, leading to an increase in heritability in the post-reform cohort (44 vs. 67%) for males. Unstandardized estimates of genetic variance were of a similar magnitude (.56 vs. .57) between cohorts, while shared environmental variance decreased from .56 to .04. Heritability remained in the same range for women (40 vs. 34%). Our results support the role of educational policy in affecting the relative weight of genetic and environmental factors on educational attainment, such that increasing equality in educational opportunities increases heritability estimates by reducing variation of non-genetic familial origin.

Show MeSH
Related in: MedlinePlus