During the study selection procedure, the reviewers concluded that all twin studies were based on community samples in which obsessive-compulsive symptoms (OCS) were not systematically assessed by standardized instruments and or direct interviews. This means that twin and population-based studies would have been excluded from the analysis, despite presenting extremely relevant information. Instead, we made the post hoc decision to wave this inclusion criterion for those studies (i.e., probands and FDRs were not directly interviewed).
