Economic disadvantage is widespread in the Southeastern coastal plain, leading many African American youth living in the Southeast to experience a range of stressful, recurrent, and uncontrollable difficulties at developmentally sensitive stages. This context may also influence outcomes and potentiate negative effects of carrying the “s” allele for SLC6A4 (Beach et al., 2014). Accordingly, experience of SES related adversity during early development is controlled in all analyses. Similarly, a range of circumstances may give rise to variation in the proportion of different cell types in the blood samples used to assess methylation (Beach et al., 2015), and it is important to control such variability in analyses linking environments to change in methylation of particular genetic regions. Accordingly, controls for cell-type variability are also included in all analyses. Finally, there is the potential for cryptic population stratification to better account for effects than does a specific genotype, and so we also include a control for ancestry informative genetic markers in the current analyses. Likewise, controls for age and sex are included in all analyses.
