Findings from epidemiological surveys in the United States and around the world have consistently shown a high prevalence of co-occurring childhood disorders, including oppositional defiant disorder (ODD), conduct disorder, and attention-deficit/hyperactivity disorder (ADHD; Boyle & Offord, 1991; Fergusson, Horwood, & Lynskey, 1994; Ford, Goodman, & Meltzer, 2003; Kandel et al., 1997). This pattern is generally mirrored by findings from clinical research (Biederman, Newcorn, & Sprich, 1991; Crowley & Riggs, 1995; Farrington & Van Kammen, 1990; Lahey, Loeber, Burke, Rathouz, & McBurnett, 2002).
