Edited by Bruce S. McEwen, The Rockefeller University, New York, NY, and approved May 16, 2017 (received for review December 15, 2016)
There is a previously well-established relationship between socioeconomic status and cognitive ability. By having access to repeated measures of cognitive data across the second part of the life span, we were able not only to study the influence of childhood social class on mean-level cognitive performance, but also on change over time. Using reared-apart monozygotic and dizygotic twins and a control sample of twins reared together, we studied the effects of childhood socioeconomic environment on cognition in later life. We found an association between childhood social class and mean levels of cognitive performance, but not longitudinal trajectories of change. When controlling for genetic influences, there was no association of childhood social class and cognitive performance late in life.
In this report we analyzed genetically informative data to investigate within-person change and between-person differences in late-life cognitive abilities as a function of childhood social class. We used data from nine testing occasions spanning 28 y in the Swedish Adoption/Twin Study of Aging and parental social class based on the Swedish socioeconomic index. Cognitive ability included a general factor and the four domains of verbal, fluid, memory, and perceptual speed. Latent growth curve models of the longitudinal data tested whether level and change in cognitive performance differed as a function of childhood social class. Between–within twin-pair analyses were performed on twins reared apart to assess familial confounding. Childhood social class was significantly associated with mean-level cognitive performance at age 65 y, but not with rate of cognitive change. The association decreased in magnitude but remained significant after adjustments for level of education and the degree to which the rearing family was supportive toward education. A between-pair effect of childhood social class was significant in all cognitive domains, whereas within-pair estimates were attenuated, indicating genetic confounding. Thus, childhood social class is important for cognitive performance in adulthood on a population level, but the association is largely attributable to genetic influences.
Author contributions: M.E., C.L., S.F., A.K.D.A., and N.L.P. designed research; M.E. and N.L.P. performed research; C.L., C.Z., and C.A.R. contributed new reagents/analytic tools; M.E. analyzed data; and M.E., S.F., A.K.D.A., C.A.R., and N.L.P. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Data deposition: The raw data reported in this paper have been deposited in the National Archive of Computerized Data on Aging, https://www.icpsr.umich.edu/icpsrweb/NACDA (accession no. ICPSR 3843). The data code for the analyses in this study is available on figshare at https://doi.org/10.6084/m9.figshare.c.3794695.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1620603114/-/DCSupplemental.
Freely available online through the PNAS open access option.
