“…However, externalizing symptoms also can be related to exuberance and approach behavior (e.g., Fox, Henderson, Rubin, Calkins, & Schmidt, 2001), which could fuel children's readiness to partake in new and arousing situations (e.g., saliva collection), which in turn could override or temper a tendency toward noncompliance. We note that externalizing and internalizing symptoms have been related to cortisol levels in young children, although results of previous studies have not been consistent (e.g., Alink et al, 2008;Eisenberg et al, 2010;Gunnar et al, 2009;Ruttle et al, 2011). We also note that externalizing and internalizing disorders are frequently comorbid, although there is evidence that their trajectories and predisposing factors may differ, at least in some children (review in Oland & Shaw, 2005).…”