In subsidiary analyses, the effect of abortion history on reproductive timing was examined using data from a subsample of female respondents with non-missing questionnaire data (nCohort I = 3576, nCohort II = 1009). For each cohort, log-rank tests were used to identify significant differences in equality of survivor functions by abortion history. Subsidiary analyses of genetic influences contributing to observed associations between reproductive timing and AD were conducted using data from complete pairs of monozygotic (MZ) and dizygotic (DZ) twins (Cohort I: nfemale MZ = 858, nmale MZ = 363, nfemale DZ = 476, nmale DZ = 194, nopposite-sex DZ = 519; Cohort II: nfemale MZ = 676, nmale MZ = 475, nfemale DZ = 491, nmale DZ = 376, nopposite-sex DZ = 635). The following variables were modeled as time-invariant predictors of eproductive onset in genetically-informed Cox analyses: AD, zygosity, cotwin AD, the interaction between zygosity and cotwin AD (a test of genetic effects), cotwin sex, and the interaction of zygosity, cotwin AD, and cotwin sex (a test of sex differences in genetic effects).
