Bendiksen, B.; Aase, H.; Svensson, E.; Friis, S.; Myhre, A. M.; Reichborn-Kjennerud, T.; Zeiner, P. Impairment in Young Preschool Children With Symptoms of Attention-Deficit/Hyperactivity Disorder and Co-Occurring Oppositional Defiant Disorder and Conduct Disorder. Scand J Child Adolesc Psychiatry Psychol 2014, 2, 95-105.