title: Scoring based on item response theory did not alter the measurement ability of EORTC QLQ-C30 scales.
abstract: OBJECTIVE
  Most health-related quality-of-life questionnaires include multi-item scales. Scale scores are usually estimated as simple sums of the item scores. However, scoring procedures utilizing more information from the items might improve measurement abilities, and thereby reduce the needed sample sizes. We investigated whether item response theory (IRT)-based scoring improved the measurement abilities of the EORTC QLQ-C30 physical functioning, emotional functioning, and fatigue scales.
  
  
  METHODS
  Using a database of 13,010 subjects we estimated the relative validities of IRT scoring compared to sum scoring of the scales.
  
  
  RESULTS
  The mean relative validities were 1.04 (physical), 1.03 (emotional), and 0.97 (fatigue). None of these were significantly larger than 1. Thus, no gain in measurement abilities using IRT scoring was found for these scales. Possible explanations include that the items in the scales are not constructed for IRT scoring and that the scales are relatively short.
  
  
  CONCLUSIONS
  IRT scoring of the three longest EORTC QLQ-C30 scales did not improve measurement abilities compared to the traditional sum scoring of the scales.
authors.affiliation: The research unit, Department of Palliative Medicine, Bispebjerg Hospital, Bispebjerg bakke 23, 2400 Copenhagen, Denmark. map01@bbh.hosp.dk
authors.forename: Morten Aa
authors.initials: MA
authors.lastname: Petersen
authors.forename: Mogens
authors.initials: M
authors.lastname: Groenvold
authors.forename: Neil
authors.initials: N
authors.lastname: Aaronson
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Brenne
authors.forename: Peter
authors.initials: P
authors.lastname: Fayers
authors.forename: Julie Damgaard
authors.initials: JD
authors.lastname: Nielsen
authors.forename: Mirjam
authors.initials: M
authors.lastname: Sprangers
authors.forename: Jakob B
authors.initials: JB
authors.lastname: Bjorner
mesh_terms: D000328:Adult; D016208:Databases, Factual; D004644:Emotions; D005221:Fatigue; D005260:Female; D006304:Health Status; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009367:Neoplasm Staging; D009369:Neoplasms / Q000503:physiopathology / Q000523:psychology; D011788:Quality of Life; D015203:Reproducibility of Results; D018401:Sample Size; D011795:Surveys and Questionnaires