The Australian twin registry (QIMR) was initiated in 1978. Temperament questionnaires were sent to two cohorts of Australian twins and their families (parents, children, spouses and siblings), the first in 1988 and the second in 1990. A total of 20 464 individuals had valid phenotypic data, and of these 5117 were genotyped and passed QC (1727 males and 3390 females, from 2567 independent families). The mean age of the participants was 36.2 (±12.1) years. The effective sample size (that is, correcting for non-independence of family members) was calculated to be 4312. Verweij et al.18 used this sample in their GWAS of TCI scales.19
