Much research has focused on early temperament as a predictor of the development of an anxiety disorder during childhood or adolescence. In particular, toddlers who are withdrawn and inhibited when encountering new people or situations have an increased risk for anxiety (Zahn-Waxler, Klimes-Dougan, & Slattery, 2000). Temperament is defined as stable moods and behaviors that can be observed in early childhood. Temperament is controlled, in part, by biology, and is the result of the environment acting on the genetic predispositions with which children are born with. By age two, when encountering unfamiliar people or situations, inhibited children will interrupt ongoing behavior, cease vocalizing, seek comfort, or withdraw. Uninhibited children will approach unfamiliar people or objects, and be outgoing and talkative (Schwartz, Snidman, & Kagan, 1999). To highlight one study of early temperament, Schwartz, Snidman, and Kagan (1999) looked at the antecedents of anxiety in adolescents in a longitudinal study. The sample consisted of 79 adolescents with a mean age of 13 years. Participants were predominantly Caucasian American and middle class. They had been categorized 12 years earlier as inhibited or uninhibited, and were then assessed at age 13 using an interview and an observation of their behavior. The interview was used to assess four domains of past and current anxiety symptoms (specific fears, separation anxiety, performance anxiety, and generalized social anxiety). During the observations, participants' frequency of spontaneous comments and smiles were counted during a one-hour session. The authors found no differences between the two groups (inhibited toddlers and uninhibited toddlers) on the measures of specific fears, separation anxiety, or performance anxiety. However, significant differences were found in social anxiety-61% of inhibited toddlers vs. 27% of uninhibited toddlers had developed generalized social anxiety by adolescence. Furthermore, during the observations, adolescents who had been classified as inhibited as toddlers made fewer spontaneous comments. Differences were more pronounced in girls than in boys. The authors concluded that an inhibited temperament in toddlerhood predisposes an adolescent to develop social anxiety, whereas an uninhibited temperament acts to protect the adolescent.