Extended Data Fig. 2: Impact of sociodemographic covariates on brain-wide association effect sizes.

The influence of sociodemographic covariates (race, gender, parental marital status, parental income, hispanic versus non-hispanic ethnicity, family, data collection site) on BWAS (brain-wide association studies) effect sizes was examined in the ABCD Study dataset (n = 3,587 with complete cases for this analysis) through the model comparison strategy developed by the ABCD Data Analysis and Informatics Core and used in the Data Exploration and Analysis Portal (deap.nimhda.org). The percentages of variance explained by fixed effects in multilevel models (pseudo-R²) were calculated with the MuMIn package in R (1.43.17) and square root transformed to approximate an absolute-value BWAS correlation (|r|). The estimated BWAS effect sizes (|r|) prior to covariate adjustment are plotted on the x-axis and those after sociodemographic covariate adjustment on the y-axis. Values below the identity line indicate a reduction in effect size after covariate adjustment, values above an increase in effect size. BWAS models with and without covariate adjustment always included cognitive ability or psychopathology as the outcome variable and nested random effects of family and data collection site, in order to maximize comparability for subsequent fixed effects model comparisons. BWAS effect sizes without covariate adjustment were taken from models that only included these random effects, the brain feature of interest (cortical thickness [vertex]/RSFC [edge]) as a single fixed effect, and the psychological phenotype (cognitive ability/psychopathology). BWAS effect sizes without covariate adjustment estimated the unique, covariate-adjusted effect linking the brain feature of interest to the psychological phenotype by comparing a model with sociodemographic fixed effects but no brain feature fixed effect, to one with both the sociodemographic fixed effects and the brain feature. The difference in pseudo-R² (subsequently transformed to |r|) represents the additional fixed-effect variance the brain feature explained beyond the sociodemographic covariates.