Hanscombe, Ken B., Trzaskowski, Maciej, Haworth, Claire M. A., Davis, Oliver S. P., Dale, Philip S. and Plomin, Robert (2012) Socioeconomic status (SES) and children's intelligence (IQ) : in a UK-representative sample SES moderates the environmental, not genetic, effect on IQ. PLoS One, Volume 7 (Number 2). Article number e30320. doi:10.1371/journal.pone.0030320 ISSN 1932-6203.

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Abstract

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.

Item Type:	Journal Article
Subjects:	B Philosophy. Psychology. Religion > BF Psychology
Divisions:	Faculty of Science, Engineering and Medicine > Science > Psychology
Library of Congress Subject Headings (LCSH):	Children -- Social conditions, Children -- Economic conditions, Children -- Intelligence levels
Journal or Publication Title:	PLoS One
Publisher:	Public Library of Science
ISSN:	1932-6203
Official Date:	1 February 2012
Dates:	Date Event 1 February 2012 Published 16 December 2011 Accepted 4 August 2011 Submitted
Volume:	Volume 7
Number:	Number 2
Number of Pages:	16
Article Number:	Article number e30320
DOI:	10.1371/journal.pone.0030320
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Open Access (Creative Commons)
Date of first compliant deposit:	28 December 2015
Date of first compliant Open Access:	28 December 2015
Funder:	Medical Research Council (Great Britain) (MRC), National Institutes of Health (U.S.) (NIH), Wellcome Trust (London, England)
Grant number:	G0500079 (MRC), HD44454 (NIH), HD46167 (NIH), G0802681 (ESRC), WT088984 (WT)

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