The main strengths of this study include the uniquely large population-based cohorts of OCD and TD/CTD patients, which generally provided sufficient power to address the primary study questions, the inclusion of different kinds of biological relatives with differing degrees of shared genetic liability and shared environment, the long-term perspective (most previous studies have been cross-sectional), and the fact that the Swedish ICD codes for OCD, TD/CTD, and many of the AD have been formally validated.25, 29, 32, 33
