The above associations were estimated after adjusting all variables for age, sex, age-sex interaction, head motion and head size (“de-confounding”). Some factors can be unambiguously considered a confound to be removed (e.g., head motion, which can corrupt IDPs but also correlates with disease/aging26). For other factors (e.g., age), the appropriateness of de-confounding depends on the question being asked and needs to be taken into consideration when interpreting associations (see Discussion). The relationship between the correlations estimated with vs. without de-confounding (Fig 6d) demonstrates that in almost all cases the strength of association was reduced by de-confounding, in some cases being almost entirely removed (horizontal cloud around y=0).
