Previous behaviour genetic analyses of the twins and siblings in our phenotypic sample indicated broad heritability estimates of 45% and 42% for Novelty Seeking, 40% and 40% for Harm Avoidance, 35% and 38% for Reward Dependence and 35% and 35% for Persistence, for males and females respectively, with remaining variance explained by unshared environmental influences (Keller, et al., 2005). Note that Keller et al. (2005) analysed one item as contributing to the Reward Dependence scale while we assigned it to the Novelty Seeking scale in accordance to the scales’ revision. For all temperament scales, reliability and internal consistency were determined to be satisfactory to good in an earlier study using subsamples of the complete phenotypic sample (Keller, et al., 2005). The 2.1 year test-retest correlations (as tested in 881 twins) was 0.79, 0.73, 0.68, and 0.64 for Harm Avoidance, Novelty Seeking, Reward Dependence, and Persistence, respectively; Cronbach’s α (as tested in 7834 to 7862 twins and siblings) was 0.61, 0.68, 0.75, and 0.84 for Harm Avoidance, Novelty Seeking, Reward Dependence, and Persistence, respectively. These reliability and internal consistency values are in accordance with those reported in other TPQ/TCI studies (Cloninger, 1994; Cloninger, et al., 1993).
