title: Examining unidimensionality and improving reliability for the eight subscales of the SF-36 in opioid-dependent patients using Rasch analysis.
abstract: OBJECTIVE
  The Medical Outcome Study Short Form 36 (SF-36) is one of the most commonly used questionnaires for monitoring the Health-Related Quality of Life (HRQOL) of opioid-dependent patients. However, the unidimensionality and reliability of the SF-36 have not been verified in opioid-dependent patients. The aim of this study was to examine the unidimensionality and to improve the test reliability of the SF-36 for use in opioid-dependent patients.
  
  
  METHODS
  A total of 583 opioid-dependent patients were recruited in the study. Unidimensionality was examined by conducting unidimensional Rasch analysis. Item fit statistics and principle component analysis were used to check the item-model fit in each of the eight subscales of the SF-36. Reliability was evaluated by applying both unidimensional and multidimensional Rasch analyses.
  
  
  RESULTS
  After three misfitting items were excluded, the remaining items of each subscale in the SF-36 represented a single construct. The test reliabilities (0.80-0.87) yielded by the multidimensional approach were much higher than those (0.68-0.82) produced by the unidimensional approach.
  
  
  CONCLUSIONS
  The remaining 32 items of the SF-36 are appropriate for evaluating the HRQOL in opioid-dependent patients in terms of unidimensionality. Additionally, the test scores produced by the multidimensional approach were more accurate than those obtained by the unidimensional approach.
authors.affiliation: Department of Educational Psychology, Texas A&M University, 4225 TAMU, College Station, TX, 77843-4225, USA.
authors.forename: Yu-Yu
authors.initials: YY
authors.lastname: Hsiao
authors.forename: Ching-Lin
authors.initials: CL
authors.lastname: Shih
authors.forename: Wan-Hui
authors.initials: WH
authors.lastname: Yu
authors.forename: Cheng-Hsi
authors.initials: CH
authors.lastname: Hsieh
authors.forename: Ching-Lin
authors.initials: CL
authors.lastname: Hsieh
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009293:Opioid-Related Disorders / Q000188:drug therapy; D011446:Prospective Studies; D011594:Psychometrics; D058996:Quality Improvement; D011788:Quality of Life; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires / Q000592:standards*; D013624:Taiwan; D055815:Young Adult
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