Socioeconomic status as a moderator of the genetic and shared environmental influence on verbal IQ: A multilevel behavioral genetic approach

• Examined potential moderating effects of school-level SES on verbal IQ
• Lower SES resulted in greater shared environmental influence on verbal IQ.
• Higher levels of SES resulted in greater genetic influences on verbal IQ.
• Influences were concentrated in the extreme tails of the SES distribution.

An expansive literature has revealed that human intelligence is under genetic influence. In an effort to further elucidate the role of genetic influences on intelligence, studies have examined the potential role that family-level socioeconomic status (SES) plays in the moderation of genetic factors. Results have been mixed, but the majority of studies have found that genetic factors have greater influence on IQ in the presence of higher levels of SES. The current study aims to contribute to this line of research by examining the role of school-level SES in moderating genetic and environmental influences on verbal intelligence at the individual level. A sample of sibling pairs from the National Longitudinal Study of Adolescent to Adult Health (Add Health) was used to estimate a series of genetically informed multilevel statistical models. The results indicate that genetic factors have a greater influence on verbal IQ for students who attend schools with higher levels of SES, and shared environmental factors have a greater influence on verbal IQ for students who attend schools with lower levels of SES, but only at extremely high and low levels of SES (scoring within the top or bottom 10th percentiles).