Figure A.1. Variance explained by imaging site (R²).

For each feature, we calculated the coefficient of determination R² between cortical thickness and imaging site. We present the densities of R² (red lines) for the (a) EMBARC study and the (b) VDLC study. To obtain a measure of significance and to correct for multiple comparisons, we performed a one-step max R² procedure. Briefly, we permuted the site labels B = 10, 000 times, recalculated the R² values and retained the maximum R² value at each permeation. The grey densities represent the distribution of the maximum R²’s. The vertical dashed line indicates the 95% quantile of the maximum R² distribution. The features above that threshold are significant at the α = 0.05 level (shaded red area). Most features remained significant after adjustment.