Relatedly, five twin studies presented results on resemblance for AUDs in opposite-sex dizygotic (DZ) twin pairs and thus were able to test for the presence of qualitative sex effects for AUDs – that the genetic risk factors were not entirely the same in males and females. This is detected largely by comparing the magnitude of the correlation in same- v. opposite-sex DZ pairs. One study found evidence for such an effect for AUDs (Prescott et al. 1999), two did not (Heath et al. 1997; Magnusson et al. 2012), and two did not test for it (Caldwell & Gottesman, 1991; Knopik et al. 2004). Because qualitative sex effects can only be detected reliably with large samples (Prescott & Gottesman, 1993), meta-analytical methods provide an ideal procedure to evaluate evidence for this effect.
