Table 2.

Heterogeneity measures

Possible subtype	Clinical information	Register information
Tic-related OCD	Structured diagnostic interviews, including questions about lifetime occurrence of tics; medical records	National Patient Register: Lifetime diagnoses of tic disorders
Early onset OCD	Approximately half of our cohort will consist of pediatric OCD cases
OCD symptom dimensions	Clinician administered: YBOCS symptom checklist at baseline Self-report: OCI-R (adult samples) and OCI-CV (pediatric samples)
Familial vs sporadic OCD	Self-reported family history of OCD and related disorders; medical records	Multigenerational and National Patient Register: Lifetime diagnoses of OCD in 1st, 2nd and 3rd degree relatives
Family history of severe mental illness (e.g. psychosis, autism)	Self-reported family history; medical records	Multigenerational and National Patient Register: Lifetime diagnoses in first, second and third-degree relatives
Treatment refractoriness	Incomplete or no treatment response with SRIs and/or CBT, measured with the YBOCS at post-treatment, medical records