title: Signs and Symptoms of Psychotic Illness (SSPI): a rating scale.
abstract: BACKGROUND
  In the rating scales commonly used for assessing response to antipsychotic treatment, individual items embrace symptoms that apparently arise from distinguishable pathophysiological processes and might be expected to respond differently to treatment.
  
  
  OBJECTIVE
  To test the reliability, sensitivity to change and factor structure of a new scale for the assessment of the Signs and Symptoms of Psychotic Illness (the SSPI).
  
  
  METHODS
  Interrater reliability was evaluated by determining the intraclass correlation for the ratings of 63 patients. Sensitivity to change was assessed in a longitudinal study of 33 patients. Factor structure was determined from scores for 155 patients.
  
  
  RESULTS
  The intraclass correlation was satisfactory for all individual items and excellent for the total score. Scores were sensitive to change. A change in Clinical Global Impression of one unit corresponded to an SSPI total score change of 31%. Factor analysis revealed five clusters of symptoms.
  
  
  CONCLUSIONS
  The SSPI provides a sensitive and reliable measure of the five major clusters of symptoms that occur commonly in psychotic illness.
authors.affiliation: Department of Psychiatry, University of British Columbia, Canada. peter.liddle@nottingham.ac.uk
authors.forename: Peter F
authors.initials: PF
authors.lastname: Liddle
authors.forename: Elton T C
authors.initials: ET
authors.lastname: Ngan
authors.forename: Gary
authors.initials: G
authors.lastname: Duffield
authors.forename: King
authors.initials: K
authors.lastname: Kho
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Warren
mesh_terms: D000208:Acute Disease; D000293:Adolescent; D000328:Adult; D002908:Chronic Disease; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011569:Psychiatric Status Rating Scales; D011618:Psychotic Disorders / Q000175:diagnosis*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity