title: Use of item response theory to develop a shortened version of the EORTC QLQ-C30 emotional functioning scale.
abstract: BACKGROUND
  As part of a larger study whose objective is to develop an abbreviated version of the EORTC QLQ-C30 suitable for research in palliative care, analyses were conducted to determine the feasibility of generating a shorter version of the 4-item emotional functioning (EF) scale that could be scored in the original metric.
  
  
  METHODS
  We used data from 24 European cancer studies conducted in 10 different languages (n = 8242). Item selection was based on analyses by item response theory (IRT). Based on the IRT results, a simple scoring algorithm was developed to predict the original 4-item EF sum scale score from a reduced number of items.
  
  
  RESULTS
  Both a 3-item and a 2-item version (item 21 'Did you feel tense?' and item 24 'Did you feel depressed?') predicted the total score with excellent agreement and very little bias. In group comparisons, the 2-item scale led to the same conclusions as those based on the original 4-item scale with little or no loss of measurement efficiency.
  
  
  CONCLUSIONS
  Although these results are promising, confirmatory studies are needed based on independent samples. If such additional studies yield comparable results, incorporation of the 2-item EF scale in an abbreviated version of the QLQ-C30 for use in palliative care research settings would be justified. The analyses reported here demonstrate the usefulness of the IRT-based methodology for shortening questionnaire scales.
authors.affiliation: Quality Metric Incorporated, Lincoln, RI 02865, USA. jbjorner@qualitymetric.com
authors.forename: J B
authors.initials: JB
authors.lastname: Bjorner
authors.forename: M Aa
authors.initials: MA
authors.lastname: Petersen
authors.forename: M
authors.initials: M
authors.lastname: Groenvold
authors.forename: N
authors.initials: N
authors.lastname: Aaronson
authors.forename: M
authors.initials: M
authors.lastname: Ahlner-Elmqvist
authors.forename: J I
authors.initials: JI
authors.lastname: Arraras
authors.forename: A
authors.initials: A
authors.lastname: Brédart
authors.forename: P
authors.initials: P
authors.lastname: Fayers
authors.forename: M
authors.initials: M
authors.lastname: Jordhoy
authors.forename: M
authors.initials: M
authors.lastname: Sprangers
authors.forename: M
authors.initials: M
authors.lastname: Watson
authors.forename: T
authors.initials: T
authors.lastname: Young
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D005060:Europe; D005240:Feasibility Studies; D006305:Health Status Indicators; D006801:Humans; D016013:Likelihood Functions; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000473:pathology / Q000523:psychology*; D010166:Palliative Care; D011788:Quality of Life; D011795:Surveys and Questionnaires