(87.2 for men, 89.5 for women), DZ twins somewhat higher (94.0 for men and 94.3 for women), while the small number of twins with unknown zygosity had higher than expected mortality (SMR for men was 113 based on 810 deaths and for women the SMR of 108 was based on 507 deaths). The unknown zygosity group includes those who had not replied to our questionnaires with zygosity items, had left the zygosity items unanswered or whose responses were conflicting such that the zygosity determination algorithm left them unclassified as to being MZ or DZ.
