a one‐stage approach (Boedhoe et al., 2019). In the two‐stage approach, IPD are first analyzed for each sample separately to obtain summary results (e.g., effect size estimates, confidence intervals, and so on), which are then used for standard meta‐analysis. In contrast, the one‐stage approach analyzes all IPD in one statistical model, while accounting for site effects, to estimate the overall effect. In the ENIGMA‐OCD publications we call the two‐stage approach meta‐analysis, and the one‐stage approach mega‐analysis. Whereas in OBIC we conducted mega‐analyses on the raw MRI data—all processed at a single site—in ENIGMA‐OCD we conducted both the two‐stage aggregated data meta‐analyses and the one‐stage IPD‐based mega‐analyses.
