For the Extraversion analysis, all Extraversion items from the NEO, IPIP and Eysenck inventories were analyzed, a selection of Reward Dependence (RD) items from the TCI, and the Positive Emotionality (PEM) items from the MPQ. Extraversion sum scores derived from the NEO, IPIP and Eysenck inventories correlate highly across inventories (Aluja et al. 2004; Draycott and Kline 1995; Larstone et al. 2002). The relationship between Extraversion and the temperament traits is less clear, but Extraversion correlates strongest with RD (De Fruyt et al. 2000; Gillespie et al. 2001). Based on the item correlations among the RD items with the Extraversion items from the NEO-PI-R and EPQ in the HBCS, PAGES and QIMR adults cohorts, we decided to include a subset of RD items that correlated strongest with the Extraversion items (see Supplementary Fig. 3 for number of items included and Supplementary Table 2 for overview of the items).
