title: Test of four hypotheses for the comorbidity of attention-deficit hyperactivity disorder and conduct disorder.
abstract: OBJECTIVE
  To study the basis of the comorbidity of two common psychiatric disorders of childhood: attention-deficit hyperactivity disorder (ADHD) and conduct disorder (CD).
  
  
  METHODS
  Subjects were 45 boys (aged 7 to 11 years) with either ADHD, CD, or ADHD + CD and 16 normal control children (NC) studied by means of a 2 (ADHD versus no ADHD) x 2 (CD versus no CD) design. We (1) tested whether similar or different patterns of cognitive, developmental risk, and psychosocial factors characterize the "pure" forms of the two disorders (i.e., ADHD and CD), and (2) compared the profile of the comorbid group (ADHD + CD) with those of the two pure groups.
  
  
  RESULTS
  The ADHD group was significantly impaired on cognitive measures (inhibitory control and response alteration) and had greater delay in development and greater reading problems compared with CD and NC children; the CD group was exposed to significantly greater environmental adversity and had more severe problems in arithmetic than the ADHD and NC groups. The ADHD+CD group was similar to the ADHD group on cognitive, developmental, and reading measures and similar to the CD group on psychosocial and arithmetic measures.
  
  
  CONCLUSIONS
  These results support the distinctiveness of ADHD and CD and the hypothesis that the comorbid condition of ADHD + CD is a hybrid of pure ADHD and pure CD.
authors.affiliation: Department of Child and Adolescent Psychiatry, Hospital for Sick Children, Toronto, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Schachar
authors.forename: R
authors.initials: R
authors.lastname: Tannock
mesh_terms: D001289:Attention Deficit Disorder with Hyperactivity / Q000150:complications* / Q000175:diagnosis; D002648:Child; D002653:Child Behavior Disorders / Q000150:complications* / Q000175:diagnosis; D003071:Cognition; D015897:Comorbidity; D005260:Female; D006801:Humans; D008297:Male; D011569:Psychiatric Status Rating Scales; D011932:Reading; D012307:Risk Factors; D011795:Surveys and Questionnaires