title: Severity of thought disorder predicts psychosis in persons at clinical high-risk.
abstract: BACKGROUND
  Improving predictive accuracy is of paramount importance for early detection and prevention of psychosis. We sought a symptom severity classifier that would improve psychosis risk prediction.
  
  
  METHODS
  Subjects were from two cohorts of the North American Prodrome Longitudinal Study. All subjects met Criteria of Psychosis-Risk States. In Cohort-1 (n=296) we developed a classifier that included those items of the Scale of Psychosis-Risk Symptoms that best distinguished subjects who converted to psychosis from nonconverters, with performance initially validated by randomization tests in Cohort-1. Cohort-2 (n=592) served as an independent test set.
  
  
  RESULTS
  We derived 2-Item and 4-Item subscales. Both included unusual thought content and suspiciousness; the latter added reduced ideational richness and difficulties with focus/concentration. The Concordance Index (C-Index), a measure of discrimination, was similar for each subscale across cohorts (4-Item subscale Cohort-2: 0.71, 95% CI=[0.64, 0.77], Cohort-1: 0.74, 95% CI=[0.69, 0.80]; 2-Item subscale Cohort-2: 0.68, 95% CI=[0.3, 0.76], Cohort-1: 0.72, 95% CI=[0.66-0.79]). The 4-Item performed better than the 2-Item subscale in 742/1000 random selections of 80% subsets of Cohort-2 subjects (p-value=1.3E-55). Subscale calibration between cohorts was proportional (higher scores/lower survival), but absolute conversion risk predicted from Cohort-1 was higher than that observed in Cohort-2, reflecting the cohorts' differences in 2-year conversion rates (Cohort-2: 0.16, 95% CI=[0.13, 0.19]; Cohort-1: 0.30, 95% CI=[0.24, 0.36]).
  
  
  CONCLUSIONS
  Severity of unusual thought content, suspiciousness, reduced ideational richness, and difficulty with focus/concentration informed psychosis risk prediction. Scales based on these symptoms may have utility in research and, assuming further validation, eventual clinical applications.
authors.affiliation: Department of Psychiatry, University of North Carolina, Chapel Hill, United States. Electronic address: Diana_Perkins@unc.edu.
authors.forename: Diana O
authors.initials: DO
authors.lastname: Perkins
authors.affiliation: Renaissance Computing Institute, University of North Carolina, Chapel Hill, NC, United States.
authors.forename: Clark D
authors.initials: CD
authors.lastname: Jeffries
authors.affiliation: Department of Psychiatry, Zucker Hillside Hospital, Long Island, NY, United States.
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Cornblatt
authors.affiliation: Department of Psychiatry, Yale University, New Haven, CT, United States.
authors.forename: Scott W
authors.initials: SW
authors.lastname: Woods
authors.affiliation: Hotchkiss Brain Institute, Department of Psychiatry, University of Calgary, Alberta, Canada.
authors.forename: Jean
authors.initials: J
authors.lastname: Addington
authors.affiliation: Department of Psychiatry and Biobehavioral Sciences, UCLA, Los Angeles, CA, United States; Department of Psychology, UCLA, Los Angeles, CA, United States.
authors.forename: Carrie E
authors.initials: CE
authors.lastname: Bearden
authors.affiliation: Department of Psychiatry, UCSD, San Diego, CA, United States.
authors.forename: Kristin S
authors.initials: KS
authors.lastname: Cadenhead
authors.affiliation: Department of Psychiatry, Yale University, New Haven, CT, United States; Department of Psychology, Yale University, New Haven, CT, United States.
authors.forename: Tyrone D
authors.initials: TD
authors.lastname: Cannon
authors.affiliation: National Institute of Mental Health, United States.
authors.forename: Robert
authors.initials: R
authors.lastname: Heinssen
authors.affiliation: Department of Psychiatry, UCSF, San Francisco, CA, United States.
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Mathalon
authors.affiliation: Department of Psychiatry, Harvard Medical School at Beth Israel Deaconess Medical Center, Boston, MA, United States; Department of Psychiatry, Massachusetts General Hospital, Boston, MA, United States.
authors.forename: Larry J
authors.initials: LJ
authors.lastname: Seidman
authors.affiliation: Department of Psychiatry, UCSD, San Diego, CA, United States.
authors.forename: Ming T
authors.initials: MT
authors.lastname: Tsuang
authors.affiliation: Department of Psychology, Emory University, Atlanta, GA, United States; Department of Psychiatry, Emory University, Atlanta, GA, United States.
authors.forename: Elaine F
authors.initials: EF
authors.lastname: Walker
authors.affiliation: Department of Psychiatry, Yale University, New Haven, CT, United States.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: McGlashan
mesh_terms: D000293:Adolescent; D003072:Cognition Disorders / Q000175:diagnosis / Q000209:etiology*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D009483:Neuropsychological Tests; D011569:Psychiatric Status Rating Scales; D011618:Psychotic Disorders / Q000150:complications* / Q000523:psychology; D012372:ROC Curve; D015203:Reproducibility of Results; D012307:Risk Factors; D016019:Survival Analysis; D013850:Thinking / Q000502:physiology*; D055815:Young Adult
keywords: High-risk; Psychosis; Risk prediction; Schizophrenia; Survival; Symptom severity