title: Application of item response theory to quantify substance use disorder severity.
abstract: OBJECTIVE
  The present investigation had two main goals: (1) Determine whether binary substance use disorder (SUD) diagnoses are indicators of a unidimensional trait indexing severity of disorder; and, (2) demonstrate the predictive, concurrent and construct validity of the SUD severity scale.
  
  
  METHODS
  Boys and their biological parents were administered structured diagnostic interviews to diagnose SUD. Item response theory (IRT) was applied to determine whether the diagnoses are indicators of a unidimensional trait. The score on this scale was correlated with substance use behavior, violence, treatment history, risky sex, and social adjustment.
  
  
  RESULTS
  SUD diagnoses are indicators of a unidimensional latent trait. Maternal and paternal SUD severity predicted son's SUD severity at age 19. The score on the SUD severity scale correlated with drug use frequency, number of different drugs used in lifetime, treatment seeking, illegal behavior, social maladjustment, and risky sex.
  
  
  CONCLUSIONS
  SUD can be quantified on an interval scale indexing severity of disorder. The advantages of measuring SUD severity as a continuous trait are discussed.
authors.affiliation: Center for Education and Drug Abuse Research, Department of Pharmaceutical Sciences, School of Pharmacy, University of Pittsburgh, 711 Salk Hall, Pittsburgh, PA 15261, USA. levent@pitt.edu
authors.forename: Levent
authors.initials: L
authors.lastname: Kirisci
authors.forename: Ralph E
authors.initials: RE
authors.lastname: Tarter
authors.forename: Michael
authors.initials: M
authors.lastname: Vanyukov
authors.forename: Chris
authors.initials: C
authors.lastname: Martin
authors.forename: Ada
authors.initials: A
authors.lastname: Mezzich
authors.forename: Stacy
authors.initials: S
authors.lastname: Brown
mesh_terms: D000328:Adult; D002648:Child; D016241:Child of Impaired Parents / Q000523:psychology; D003415:Crime / Q000523:psychology; D017831:Diagnosis, Dual (Psychiatry); D039721:Diagnostic and Statistical Manual of Mental Disorders; D005192:Family Health; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D001523:Mental Disorders / Q000175:diagnosis / Q000523:psychology; D015233:Models, Statistical; D011594:Psychometrics; D012309:Risk-Taking; D012720:Severity of Illness Index; D012725:Sexual Behavior / Q000523:psychology; D012917:Social Adjustment; D019966:Substance-Related Disorders / Q000175:diagnosis* / Q000523:psychology; D014754:Violence / Q000523:psychology