Temperament in all samples was assessed using Cloninger's TCI.4 The QIMR sample used a short version (54 dichotomous items26) of the Tridimensional Personality Questionnaire (TPQ) subset of the TCI. Although the TPQ originally measured three dimensions, revisions showed that five items contributing to RD should be analyzed as a separate P scale, and that one of the RD items should be assigned to NS. Therefore, the final TPQ measure as obtained in the QIMR sample included 18 HA, 19 NS, 12 RD and 5 P items. For each scale, missing items were replaced with the mean item score. If individuals had >25% of the scales' items missing, their scale score was treated as missing. Scale scores were transformed by taking the arcsine of the square root, corrected for the linear combination of age, age-squared, sex, a sex by age interaction and a sex by age-squared interaction, and standardized separately for each sex to a mean of 0 and a s.d. of 1.
