The Finnish Twin Cohort (Kaprio & Koskenvuo, 2002) includes 16 282 twin pairs alive and aged at least 18 years in 1975. The cohort is made up of 4184 monozygotic (MZ) and 9257 dizygotic (DZ) pairs, with 2841 of unconfirmed zygosity due to non-response or inconsistency in response to zygosity queries, is 49.4% female and had an average age of 35.1 years in 1974. Cohort members received extensive health questionnaires in 1975 and 1981. Response rates were 89% and 84%, respectively.
