title: Reducing outcome measures in mental health: a systematic review of the methods.
abstract: BACKGROUND
  Traditionally, classical test theory (CTT) has been used for instrument development and various methods have since been proposed for reducing outcome measures to shorter versions. These reduction methods have not previously been compared in mental or physical health.
  
  
  OBJECTIVE
  To identify and compare the various methods used to develop brief versions of outcome measures from existing measures in mental health.
  
  
  METHODS
  A systematic review of the literature in Embase, Medline, PsychInfo and from a grey literature was done. Search strategies were developed in each database to identify all relevant literature based on the inclusion criteria. Each paper identified was briefly described and then assessed using a bespoke assessment checklist developed by the authors. Methods for reducing outcome measures found across all studies were compared.
  
  
  RESULTS
  Ten papers were identified. Five methods were used for scale reduction: Rasch analysis (RA), exploratory factor analysis (EFA), graded response models (GRMs), all-subset regression, and regression. RA was the most widely used process.
  
  
  CONCLUSIONS
  The Rasch model (RM) is the only model where "'specific objectivity"' is a defining property of the model. This property is necessary for constructing scales in line with the fundamental principles of measurement.
authors.affiliation: a Institute of Psychiatry , Centre for the Economics of Mental and Physical Health, King's College London , London , UK and.
authors.forename: Wayne
authors.initials: W
authors.lastname: Smith
authors.affiliation: a Institute of Psychiatry , Centre for the Economics of Mental and Physical Health, King's College London , London , UK and.|b Barts and The London School of Medicine and Dentistry , Centre for Primary Care and Public Health, Queen Mary University of London , London , UK.
authors.forename: Anita
authors.initials: A
authors.lastname: Patel
authors.affiliation: a Institute of Psychiatry , Centre for the Economics of Mental and Physical Health, King's College London , London , UK and.
authors.forename: Paul
authors.initials: P
authors.lastname: McCrone
authors.affiliation: a Institute of Psychiatry , Centre for the Economics of Mental and Physical Health, King's College London , London , UK and.
authors.forename: Huajie
authors.initials: H
authors.lastname: Jin
authors.affiliation: a Institute of Psychiatry , Centre for the Economics of Mental and Physical Health, King's College London , London , UK and.
authors.forename: Beatrice
authors.initials: B
authors.lastname: Osumili
authors.affiliation: a Institute of Psychiatry , Centre for the Economics of Mental and Physical Health, King's College London , London , UK and.
authors.forename: Barbara
authors.initials: B
authors.lastname: Barrett
mesh_terms: D006304:Health Status; D006305:Health Status Indicators; D006801:Humans; D001523:Mental Disorders / Q000628:therapy*; D008603:Mental Health; D017063:Outcome Assessment, Health Care / Q000379:methods*; D011594:Psychometrics
keywords: Outcome measures; mental health; outcomes research; questionnaire development; questionnaire reduction