Supplementary File 1 contains Tables (1–36) of all included studies for each comorbid disorder. The meta-analysis included 91 studies published over 3 decades (1992–2020). The pooled sample size of 15,808 individuals is marginally female predominant (51.5%); in both adult (females ~ 51.4%) and paediatric studies (females ~ 52.1%), in keeping with epidemiologic patterns (44, 45). Around 90% studies used the DSM-IV (46)/ICD-10 (47) or later diagnostic criteria to define OCD and comorbid disorders. There were 16 studies on paediatric OCD. Mean age varied between 11 and 15 years in the paediatric studies, and between 23 and 45 years in the adult studies. A majority of the studies reported on findings from cross-sectional assessments (66.3%). More than 30% of studies were conducted in the United States (USA), followed by Italy (10%) and The Netherlands (9%). Samples represented patients from highly developed nations such as Norway, Germany, Sweden, Australia, The Netherlands, and Denmark, as well as developing countries including South Africa and India (48). Less than 20% of the studies explicitly reported current comorbidities. We have pooled lifetime comorbidity rates in the meta-analysis.
