The analyses for this study are based on data from a total of 3527 males who completed the clinical interview, including 3004 individuals from complete pairs (860 complete monozygotic (MZ) pairs and 642 complete dizygotic pairs (DZ)) and 523 individuals whose co-twin did not participate. Twin analyses use the fact that MZ pairs are genetically identical whereas DZ twins share on average 50% of their segregating genes.
