To assess novelty seeking at age 12, each twin completed the Junior Temperament and Character Inventory (J-TCI; Luby, Svrakic, McCallum, Przybeck, & Cloninger, 1999), which consists of 18 items. Novelty seeking can be characterized as high levels of exploratory behavior, enjoyment of novel experiences, and seeking of immediate rewards. Two example items for the novelty-seeking scale of the J-TCI are “I always like to spend time thinking about what I am going to do before I do it” (reversed) and “Even if I know I could get hurt, I can easily do things that are scary and dangerous.” Previous studies have reported Cronbach’s alpha coefficients ranging from .64 to .80 and estimates of test–retest reliability from .79 to .86 (Laucht, Becker, Blomeyer, & Schmidt, 2007; Lyoo et al., 2004; Schmeck, Goth, Poustka, & Cloninger, 2001). When the twins were reassessed at age 17, they completed Cloninger’s Tridimensional Personality Questionnaire—Short Form (TPQ; Heath, Cloninger, & Martin, 1994), which also provides a measure of novelty seeking based on 18 items. Two example items for the novelty-seeking scale of the TPQ are “I
