Several studies find one factor common among mood and anxiety disorders. Using the results of the National Comorbidity Survey (Kessler et al., 1994), Krueger (1999) found support for one internalizing psychopathology factor that was common to major depressive disorder, dysthymia, generalized anxiety disorder, social phobia, specific phobia, agoraphobia, and panic disorder. The results of Krueger (1999) were replicated by Kruger and Markon (2006) in a meta-analysis of five studies. In addition, McGlinchey and Zimmerman (2007) examined psychiatric outpatients and found that one internalizing psychopathology factor was common to major depressive disorder, panic and agoraphobia, specific phobia, social phobia and generalized anxiety disorder. Finally, in a study of caretaker-reported psychopathology in twin children and adolescents, Lahey et al. (2008) found a higher-order internalizing factor that was common among mood and anxiety disorders.
