Table 2.

Results from the fully adjusted co-twin control model predicting alcohol use disorder symptoms.

Predictor	IRR (95% CI)
Sex	1.51 (1.36 – 1.67)
Zygosity	1.03 (0.93 – 1.14)
WP Age of First Drink	0.98 (0.94 – 1.01)
BP Age of First Drink	0.94 (0.91 – 0.97)
WP Age of Onset of Regular Drinking	0.95 (0.92 – 0.98)
BP Age of Onset of Regular Drinking	0.91 (0.89 – 0.94)
Household Income	0.99 (0.97 – 1.02)
Educational Attainment	0.97 (0.93 – 1.01)
Neuroticism	1.35 (1.25 – 1.45)
Agreeableness	0.82 (0.74 – 0.91)
Extraversion	1.23 (1.11 – 1.35)
Conscientiousness	0.88 (0.81 – 0.97)
Openness	0.96 (0.87 – 1.07)
Conduct Disorder Symptoms	1.15 (1.10 – 1.19)
Early Regular Smoking	0.90 (0.76 – 1.07)
Early Repeated Marijuana Use	0.96 (0.84 – 1.10)

Note: Bold indicates significance. IRR = incidence rate ratio, WP = within-twin pair (i.e., quasi-causal effect), BP = between-twin pair (i.e., familial effect).