Name: Twins data (Tvillingdata)
Period(s): 1953 (SMS)
Code book: V


The Stockholm Birth Cohort includes 144 identifiable pairs of twins. The variable “zygo” allow us to distinguish between monozygotic and dizygotic twins. There are 14 pairs of samesex twins with unknown zygoticity. There is one female twin in the data set that cannot be matched to her twin brother or sister. In general, there are more individuals identified in the delivery records (DELIV) and in the register of population and income from 1964 (REGIST) as twins. But not all of them can be matched to their twin brother or sister. The zygotivity of these twins has been determined by matching cohort members to the twins register maintained by Karolinska Institutet. They (KI) deem that monozygotic twins can be classified with up to 99 percent certainty, while dizygotic twins can be classified up to 95 percent certainty. Details concerning this procedure can be found in Fischbein and Åkerman’s (1990) Project Metropolitan Report No 29, “Tvillingar – En Riskgrupp?” (eng. = Twins – A Risk Group?), which appears to be the first report that uses this data set.