We examined differences between OCD patients and controls within a mega-analytical framework by pooling the extracted cortical thickness and surface area measures from each site. Each of the 70 cortical regions of interest (68 regions and two whole-hemisphere average thickness or total surface area measures) served as the outcome measure and a binary indicator of diagnosis as the predictor of interest in multiple linear regression models. All cortical thickness models were adjusted for age and sex; cortical surface area models were corrected for intracranial volume (ICV, see Supplementary Information SI1), age, age2, sex, age-by-sex, and age2-by-sex, to account for any higher-order effects on cortical surface area of age and sex as well as head size, which do not appear to be detectable for cortical thickness measures (22). Additionally, all models were also adjusted for site, coded by using dummy variables. Effect size estimates were calculated using the Cohen’s d metric computed from the t-statistic of the diagnosis indicator variable from the regression models. Similarly, for models testing interactions (i.e., sex-by-diagnosis and age-by-diagnosis), a multiplicative predictor was the predictor of interest with the main effect of each predictor included in the model. The effect size was calculated using the same procedure.
