title: Simple identification of complex ADHD subtypes using current symptom counts.
abstract: OBJECTIVE
  New attention-deficit/hyperactivity disorder (ADHD) subtypes identified through latent class analysis have been recently proposed. Here, we assess the accuracy of simple rules based on symptom counts for the assignment of youths to clinically relevant population-derived ADHD subtypes: severe inattentive (SI) and severe combined (SC).
  
  
  METHODS
  Data from 9,675 twins and siblings from Missouri and Australia aged 7 to 19 years were analyzed using continuous and categorical models of ADHD symptoms using principal components analysis and subtyping by DSM-IV and by latent class criteria. Cut points were derived for classifying SI and SC subtypes by positive predictive value, negative predictive value, percent positive agreement, and Matthew coefficient of agreement.
  
  
  RESULTS
  Principal components analysis suggested two underlying factors: total number of symptoms and symptom type, with SI and SC latent class subtypes clearly mapping to distinct areas on a plot of these factors. Having six or more total symptoms and fewer than three hyperactive-impulsive symptoms accurately predicts the latent class SI subtype. The latent class SC subtype was best identified by 11 or more total symptoms and 4 or more hyperactive-impulsive. The DSM-IV ADHD subtype criteria accurately identified the SC subtype but only poorly for the SI subtype.
  
  
  CONCLUSIONS
  Symptom counts criteria allow the simple and accurate identification of subjects with severe ADHD subtypes defined by latent class analysis. Such simple symptom counts corresponding to screening cut points selected latent class-derived SI subtype subjects with greater precision than DSM-IV criteria.
authors.affiliation: Dr. Volk is with the Division of Biostatistics, Department of Preventive Medicine, Keck School of Medicine, University of Southern California; Dr. Todorov is with the Department of Psychiatry, Washington University School of Medicine; Dr. Hay is with the School of Psychology, Curtin University of Technology; and Dr. Todd, deceased, was with the Department of Psychiatry and Department of Genetics at Washington University School of Medicine. Electronic address: hvolk@usc.edu.
authors.forename: Heather E
authors.initials: HE
authors.lastname: Volk
authors.affiliation: Dr. Volk is with the Division of Biostatistics, Department of Preventive Medicine, Keck School of Medicine, University of Southern California; Dr. Todorov is with the Department of Psychiatry, Washington University School of Medicine; Dr. Hay is with the School of Psychology, Curtin University of Technology; and Dr. Todd, deceased, was with the Department of Psychiatry and Department of Genetics at Washington University School of Medicine.
authors.forename: Alexandre A
authors.initials: AA
authors.lastname: Todorov
authors.affiliation: Dr. Volk is with the Division of Biostatistics, Department of Preventive Medicine, Keck School of Medicine, University of Southern California; Dr. Todorov is with the Department of Psychiatry, Washington University School of Medicine; Dr. Hay is with the School of Psychology, Curtin University of Technology; and Dr. Todd, deceased, was with the Department of Psychiatry and Department of Genetics at Washington University School of Medicine.
authors.forename: David A
authors.initials: DA
authors.lastname: Hay
authors.affiliation: Dr. Volk is with the Division of Biostatistics, Department of Preventive Medicine, Keck School of Medicine, University of Southern California; Dr. Todorov is with the Department of Psychiatry, Washington University School of Medicine; Dr. Hay is with the School of Psychology, Curtin University of Technology; and Dr. Todd, deceased, was with the Department of Psychiatry and Department of Genetics at Washington University School of Medicine.
authors.forename: Richard D
authors.initials: RD
authors.lastname: Todd