title: Application of a disease-specific mapping function to estimate utility gains with effective treatment of schizophrenia.
abstract: BACKGROUND
  Most tools for estimating utilities use clinical trial data from general health status models, such as the 36-Item Short-Form Health Survey (SF-36). A disease-specific model may be more appropriate. The objective of this study was to apply a disease-specific utility mapping function for schizophrenia to data from a large, 1-year, open-label study of long-acting risperidone and to compare its performance with an SF-36-based utility mapping function.
  
  
  METHODS
  Patients with schizophrenia or schizoaffective disorder by DSM-IV criteria received 25, 50, or 75 mg long-acting risperidone every 2 weeks for 12 months. The Positive and Negative Syndrome Scale (PANSS) and SF-36 were used to assess efficacy and health-related quality of life. Movement disorder severity was measured using the Extrapyramidal Symptom Rating Scale (ESRS); data concerning other common adverse effects (orthostatic hypotension, weight gain) were collected. Transforms were applied to estimate utilities.
  
  
  RESULTS
  A total of 474 patients completed the study. Long-acting risperidone treatment was associated with a utility gain of 0.051 using the disease-specific function. The estimated gain using an SF-36-based mapping function was smaller: 0.0285. Estimates of gains were only weakly correlated (r = 0.2). Because of differences in scaling and variance, the requisite sample size for a randomized trial to confirm observed effects is much smaller for the disease-specific mapping function (156 versus 672 total subjects).
  
  
  CONCLUSIONS
  Application of a disease-specific mapping function was feasible. Differences in scaling and precision suggest the clinically based mapping function has greater power than the SF-36-based measure to detect differences in utility.
authors.affiliation: Veterans Administration San Diego Health Care System, San Diego, California, USA. llenert@ucsd.edu
authors.forename: Leslie A
authors.initials: LA
authors.lastname: Lenert
authors.forename: Marcia F T
authors.initials: MF
authors.lastname: Rupnow
authors.forename: Christine
authors.initials: C
authors.lastname: Elnitsky
mesh_terms: D000284:Administration, Oral; D000328:Adult; D014150:Antipsychotic Agents / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D003692:Delayed-Action Preparations; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care / Q000379:methods*; D011569:Psychiatric Status Rating Scales; D011618:Psychotic Disorders / Q000175:diagnosis / Q000188:drug therapy* / Q000503:physiopathology; D011788:Quality of Life; D018967:Risperidone / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D012559:Schizophrenia / Q000175:diagnosis / Q000188:drug therapy* / Q000503:physiopathology; D018434:Sickness Impact Profile
chemical_list: D014150:Antipsychotic Agents; D003692:Delayed-Action Preparations; D018967:Risperidone