title: Assessing measurement invariance of a health-related quality-of-life questionnaire in radiotherapy patients.
abstract: OBJECTIVE
  If the assumption of measurement invariance is not tested, we cannot be sure whether differences observed are due to true differences in health-related quality-of-life (HRQoL), or are measurement artifacts. We aim to investigate this assumption in a sample of heterogeneous cancer patients, focusing on whether age, sex, previous treatment for cancer, and information regarding treatment preferences result in biased HRQoL scores.
  
  
  METHODS
  155 cancer patients who were about to begin their first session of radiotherapy were included. HRQoL was measured using the EORTC QLQ-C30. Structural equation modeling was applied to assess whether there was a violation of the assumption of invariance.
  
  
  RESULTS
  A satisfactory single construct (Functioning HRQoL) measurement model was found and two violations of invariance were identified. Irrespective of patients' Functioning HRQoL, older patients reported worse physical functioning and patients who had received treatment prior to radiotherapy reported worse emotional functioning than we would otherwise expect.
  
  
  CONCLUSIONS
  In the present study, accounting for measurement bias lead to a substantial improvement in the overall fit of the model. By ignoring the bias, we would have concluded that the model fit was unsatisfactory. The findings underline the importance of investigating measurement invariance in scales designed for heterogeneous samples.
authors.affiliation: Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands. kingkalb@tcd.ie
authors.forename: Bellinda L
authors.initials: BL
authors.lastname: King-Kallimanis
authors.forename: Claartje L
authors.initials: CL
authors.lastname: ter Hoeven
authors.forename: Hanneke C
authors.initials: HC
authors.lastname: de Haes
authors.forename: Ellen M
authors.initials: EM
authors.lastname: Smets
authors.forename: Caro C E
authors.initials: CC
authors.lastname: Koning
authors.forename: Frans J
authors.initials: FJ
authors.lastname: Oort
mesh_terms: D000368:Aged; D005260:Female; D006304:Health Status; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000523:psychology* / Q000532:radiotherapy*; D011788:Quality of Life; D011878:Radiotherapy / Q000523:psychology*; D011795:Surveys and Questionnaires