The tetrachoric cross-twin correlations are shown in Table 4. The cross twin-within age correlations (presented at the diagonal in italic) showed a different pattern for MZ and DZ twins. MZ correlations were of similar magnitude for the ages 18–29: .40–.50 for MZF and .50–.60 for MZM. At age 15–17 the correlations were somewhat higher (r MZM = .73; r MZF = .54) and for MZM at age 30–32 somewhat lower (.35). DZ correlations started high at age 15–17 (r DZM = .68; r DZF = .56; r DOS = .48), but were much lower at later ages. This was seen most clearly for DZM, but was also true for DZF and DOS twins. This pattern suggests the influence of shared environmental factors at younger ages and the increase of importance of genetic influences over time.Table 4Estimates of tetrachoric correlationsa (with standard errors) for the CAGE as dichotomy (0 vs. 1+ yes answers)MZM15–1718–2021–2324–2627–2930–32DZM15–1718–2021–2324–2627–2930–3215–17 .73 (.14) 15–17 .68 (.17) 18–20.29 (.18) .50 (.10) 18–20.19 (.22) .32 (.13) 21–23.19 (.21).43 (.10) .57 (.08) 21–23.11 (.26)−.10 (.16) .08 (.14) 24–26.09 (.24).26 (.11).33 (.09) .59
