We carried out a comprehensive search according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (35) across four databases–PubMed, Scopus, PsycINFO, and EMBASE. We looked for studies published between 1979 and October 2020 in keeping with the publication timelines for ICD-9 (36)/DSM-III (37) using a title search for terms “obsessive compulsive disorder,” “OCD,” “obsessive compulsive,” and “OC.” We looked at clinic or community based original studies published in English, meeting the following inclusion criteria: (i) OCD diagnosis meeting criteria on ICD-9/DSM-III or later versions, (ii) Diagnosis ascertained using standardised diagnostic interviews/instruments, (iii) OCD sample size ≥100, (iv) Reporting prevalence of comorbid disorders in frequency/percentages. Included studies were required to have at least 100 individuals with diagnosed OCD, in order to detect comorbidities at a least rate of 1%. Studies with comorbidity-based selection of participants were excluded. The protocol for this systematic review has been published on the International Prospective Register of Systematic Reviews (PROSPERO) (ID: CRD42020215904). Search results were imported into Covidence software (Veritas Health Innovation, n.d.) and all stages of screening and data extraction were
