Information about relatives was derived from the Multi-Generation Register, which contains information about biological parents of an index person. A prerequisite for being included in the register is that the index person was born after January 1, 1932 and ever registered as living in Sweden after 1960. For immigrants to Sweden, similar information exists for those who became citizens before 18 years of age together with one or both parents. The biological father of the offspring is assumed to be the husband of the mother at the time of birth or identified “by acknowledgment” for unwed mothers.24
