Socioeconomic Status (SES) and Children's Intelligence (IQ): In a UK-Representative Sample SES Moderates the Environmental, Not Genetic, Effect on IQ

Background The environment can moderate the effect of genes - a phenomenon called gene-environment (GxE) interaction. Several studies have found that socioeconomic status (SES) modifies the heritability of children's intelligence. Among low-SES families, genetic factors have been reported to explain less of the variance in intelligence; the reverse is found for high-SES families. The evidence however is inconsistent. Other studies have reported an effect in the opposite direction (higher heritability in lower SES), or no moderation of the genetic effect on intelligence. Methods Using 8716 twin pairs from the Twins Early Development Study (TEDS), we attempted to replicate the reported moderating effect of SES on children's intelligence at ages 2, 3, 4, 7, 9, 10, 12 and 14: i.e., lower heritability in lower-SES families. We used a twin model that allowed for a main effect of SES on intelligence, as well as a moderating effect of SES on the genetic and environmental components of intelligence. Results We found greater variance in intelligence in low-SES families, but minimal evidence of GxE interaction across the eight ages. A power calculation indicated that a sample size of about 5000 twin pairs is required to detect moderation of the genetic component of intelligence as small as 0.25, with about 80% power - a difference of 11% to 53% in heritability, in low- (−2 standard deviations, SD) and high-SES (+2 SD) families. With samples at each age of about this size, the present study found no moderation of the genetic effect on intelligence. However, we found the greater variance in low-SES families is due to moderation of the environmental effect – an environment-environment interaction. Conclusions In a UK-representative sample, the genetic effect on intelligence is similar in low- and high-SES families. Children's shared experiences appear to explain the greater variation in intelligence in lower SES.

[1]  Robert Plomin,et al.  The Genetic and Environmental Origins of Learning Abilities and Disabilities in the Early School Years , 2013 .

[2]  S. Scarr.  Race, social class, and individual differences in I.Q , 1982 .

[3]  R. Plomin,et al.  Twins Early Development Study (TEDS): A Multivariate, Longitudinal Genetic Investigation of Language, Cognition and Behavior Problems in Childhood , 2002, Twin Research.

[4]  T. Price,et al.  Gene–environment correlations: a review of the evidence and implications for prevention of mental illness , 2007, Molecular Psychiatry.

[5]  R. Plomin,et al.  g in middle childhood: Moderate genetic and shared environmental influence using diverse measures of general cognitive ability at 7, 9 and 10 years in a large population sample of twins , 2008 .

[6]  S. Ceci,et al.  Nature-nurture reconceptualized in developmental perspective: a bioecological model. , 1994, Psychological review.

[7]  Brian D. Ripley,et al.  Modern Applied Statistics with S Fourth edition , 2002 .

[8]  G. Willemsen,et al.  Gene-Environment Interaction in Adults’ IQ Scores: Measures of Past and Present Environment , 2008, Behavior genetics.

[9]  H. Akaike.  Factor analysis and AIC , 1987 .

[10]  J. Fleiss,et al.  Intraclass correlations: uses in assessing rater reliability. , 1979, Psychological bulletin.

[11]  R Core Team,et al.  R: A language and environment for statistical computing. , 2014 .

[12]  Kenneth S Kendler,et al.  Age-Related Changes in Heritability of Behavioral Phenotypes Over Adolescence and Young Adulthood: A Meta-Analysis , 2007, Twin Research and Human Genetics.

[13]  Matt McGue,et al.  Adjustment of twin data for the effects of age and sex , 1984, Behavior genetics.

[14]  R. Plomin.  Behavioral genetics. , 1991, Research publications - Association for Research in Nervous and Mental Disease.

[15]  R. Plomin,et al.  Infant zygosity can be assigned by parental report questionnaire data. , 2000, Twin research : the official journal of the International Society for Twin Studies.

[16]  N. Bayley.  Bayley Scales of Infant Development , 1999 .

[17]  J. Raven,et al.  Manual for Raven's progressive matrices and vocabulary scales , 1962 .

[18]  R. Bradley,et al.  Socioeconomic status and child development. , 2002, Annual review of psychology.

[19]  Robert Plomin,et al.  The nature of nurture: Genetic influence on “environmental” measures , 1991, Behavioral and Brain Sciences.

[20]  Siv Fischbein,et al.  IQ and social class , 1980 .

[21]  W. Kremen,et al.  Does Parental Education have a Moderating Effect on the Genetic and Environmental Influences of General Cognitive Ability in Early Adulthood? , 2010, Behavior genetics.

[22]  Christina Gloeckner,et al.  Modern Applied Statistics With S , 2003 .

[23]  E. Lehmann,et al.  Nonparametrics: Statistical Methods Based on Ranks , 1976 .

[24]  N. Martin,et al.  The power of the classical twin study , 1978, Heredity.

[25]  R. Plomin,et al.  The Validity of a Parent-based Assessment of Cognitive Abilities in Three-year Olds* , 2002 .

[26]  R. Uher,et al.  Use of socioeconomic status in health research. , 2006, JAMA.

[27]  G. Evans.  The environment of childhood poverty. , 2004, The American psychologist.

[28]  John Fox,et al.  OpenMx: An Open Source Extended Structural Equation Modeling Framework , 2011, Psychometrika.

[29]  R. Plomin,et al.  Environmental Moderators of Genetic Influence on Verbal and Nonverbal Abilities in Early Childhood. , 2005 .

[30]  J. Steven Reznick,et al.  Short-form versions of the MacArthur Communicative Development Inventories , 2000, Applied Psycholinguistics.

[31]  L. Peltonen,et al.  Classical twin studies and beyond , 2002, Nature Reviews Genetics.

[32]  M. Rutter,et al.  Gene-environment interdependence. , 2007, Developmental science.

[33]  R. Plomin,et al.  Testing cognitive abilities by telephone in a sample of 6-to 8-year-olds , 2002 .

[34]  M. Rutter,et al.  The validity of parent-based assessment of the cognitive abilities of 2-year-olds , 1998 .

[35]  R. Plomin,et al.  Internet Cognitive Testing of Large Samples Needed in Genetic Research , 2007, Twin Research and Human Genetics.

[36]  S. Scarr,et al.  Developmental theories for the 1990s: development and individual differences. , 1992, Child development.

[37]  Lindon J. Eaves,et al.  Genotype × Environment Interaction in Psychopathology: Fact or Artifact? , 2006, Twin Research and Human Genetics.

[38]  Avshalom Caspi,et al.  Gene-environment interplay and psychopathology: multiple varieties but real effects. , 2006, Journal of child psychology and psychiatry, and allied disciplines.

[39]  E. Turkheimer,et al.  Emergence of a Gene × Socioeconomic Status Interaction on Infant Mental Ability Between 10 Months and 2 Years , 2011, Psychological science.

[40]  M. Metzler,et al.  Socioeconomic status in health research: one size does not fit all. , 2005, JAMA.

[41]  R Plomin,et al.  Genotype-environment interaction and correlation in the analysis of human behavior. , 1977, Psychological bulletin.

[42]  E. J. van den Oord,et al.  Genetic and environmental influences on vocabulary IQ: parental education level as moderator. , 1999, Child development.

[43]  R. Plomin,et al.  Twins' Early Development Study (TEDS): A Multivariate, Longitudinal Genetic Investigation of Language, Cognition and Behavior Problems from Childhood Through Adolescence , 2007, Twin Research and Human Genetics.

[44]  R. Plomin,et al.  Dramatic Increase in Heritability of Cognitive Development from Early to Middle Childhood , 2009, Psychological science.

[45]  N. Martin,et al.  The heritability of general cognitive ability increases linearly from childhood to young adulthood , 2010, Molecular Psychiatry.

[46]  S Scarr-Salapatek,et al.  Race, social class, and IQ. , 1971, Science.

[47]  K. Kendler,et al.  Interpretation of interactions: guide for the perplexed. , 2010, The British journal of psychiatry : the journal of mental science.

[48]  L J Eaves,et al.  Models for the joint effect of genotype and environment on liability to psychiatric illness. , 1986, The American journal of psychiatry.

[49]  Shaun Purcell,et al.  Variance components models for gene-environment interaction in twin analysis. , 2002, Twin research : the official journal of the International Society for Twin Studies.

[50]  J. Squires,et al.  The Asq User's Guide for the Ages & Stages Questionnaires - a Parent-completed, Child-monitoring System , 2003 .

[51]  R. Plomin,et al.  Rethinking environmental contributions to child and adolescent psychopathology: a meta-analysis of shared environmental influences. , 2009, Psychological bulletin.

[52]  I. Gottesman,et al.  PSYCHOLOGICAL SCIENCE Research Article SOCIOECONOMIC STATUS MODIFIES HERITABILITY OF IQ , 2022 .

[53]  M. Birnbaum.  Human research and data collection via the internet. , 2004, Annual review of psychology.

[54]  A. Kaufman,et al.  McCarthy Scales of Children's Abilities , 2008 .

[55]  Robert Plomin,et al.  Behavioral Genetics (5th edition) , 2008 .