A cross-national epidemiological resource: the Swedish and Finnish cohort studies of like-sexed twins.

Two large-scale studies of adult like-sexed twin pairs are ongoing in Sweden and Finland. Both studies comprise an unselected series that has been studied in a comparable fashion. Zygosity determination and health questionnaire data-gathering were carried out in 1973 for the Swedish study and in 1975 for the Finnish study for the comparable age groups. Data on hospital usage, cancer incidence and mortality are collected by record-linkage from the respective national registries. Cross-national twin studies can permit testing of hypotheses of the relationships between genetic and cultural factors and major chronic diseases and their risk factors.