We first investigated whether the CAGE was measurement invariant over age and sex. From the dataset as described above one observation per individual was selected. For individuals with repeated measures, observations were selected that gave age groups of roughly the same size. This resulted in the following 12 mutually exclusive age by sex groups: twins aged 15–17 (383 males, 691 females); twins aged 18–20 (698 males, 1,142 females); twins aged 21–23 (530 males, 754 females); twins aged 24–26 (353 males, 705 females); twins aged 27–29 (870 males, 1,487 females); twins aged 30–32 (343 males, 442 females).
