Table 2.

Parameter estimates with 95% confidence intervals for the Item Response Theory (IRT) analysis on indicators of alcohol use disorders in a sample of 1336 twin pairs from the general population who have initiated alcohol use.

	Standardized factor loading	Factor loading	Threshold #1	Threshold #2
Life-time DSM-IV alcohol dependence	0.95 (0.91 – 0.99)	5.24 (3.18 – 7.30)	6.52 (4.23 – 8.81)	-
Life-time DSM-IV alcohol abuse	0.83 (0.78 – 0.88)	2.65 (2.14 – 3.16)	3.96 (3.42 – 4.51)	-
Binge drinking: ≥5 units	0.65 (0.60 – 0.70)	1.56 (1.35 – 1.77)	1.12 (0.94 – 1.29)	3.46 (3.19 – 3.73)
Self-perceived life-time alcohol abuse	0.65 (0.60 – 0.71)	1.58 (1.35 – 1.77)	1.06 (0.89 – 1.24)	2.01 (1.80 – 2.22)

Mean for men on the AUD risk continuum was fixed to zero, and estimated to be −0.65 (−0.77 to −0.52) for women. The variance of AUD risk continuum was not different across sex, and fixed to unity. The factor loading is the increase in log-odds for the category with an increase on the factor of 1. The first threshold is the log-odds for the category when the factor is at zero. The second threshold is the increase in log-odds beyond threshold 1 for the category when the factor is at zero. The standardized factor loading is the correlation between the latent factor and the observed categorical indicator. All estimates are given with ± standard error. Thresholds for binge drinking were (#1) ‘2–4 times per month’ and (#2) ‘1–2 times per week’ or ‘more often’. For self-perceived life-time alcohol abuse, the thresholds were (#1) ‘maybe’ and (#2) ‘yes’.