title: Traditional and Rasch psychometric analyses of the Quality of Life in Adult Cancer Survivors (QLACS) questionnaire in shorter-term cancer survivors 15 months post-diagnosis.
abstract: OBJECTIVE
  The aim of this paper is to provide new insights into the psychometrics of the Quality of Life in Adult Cancer Survivors (QLACS) questionnaire, originally developed for longer-term survivors 5+years post-diagnosis. Specifically, to examine the classic psychometric properties of QLACS in a sample of shorter-term survivors, and to undertake Rasch analysis to explore the extent to which the Generic and Cancer-Specific summary scales (and separately-analysed Benefits of cancer domain) are unidimensional, with linear measurement properties and no differential item functioning (DIF).
  
  
  METHODS
  Patients with potentially curable breast, colorectal or prostate cancer completed QLACS 15 months post-diagnosis (N=407). Score distributions, floor and ceiling effects, internal reliability, and feasibility (completion time and missing data) were examined. Rasch analysis included examination of item fit, DIF and unidimensionality.
  
  
  RESULTS
  The QLACS domains and summary scales had very similar score distributions and classic psychometric properties (no ceiling effects, majority no floor effects, acceptable reliability) to those found in development work with longer-term survivors. Median completion time was 10 min and total missing data 2.3%. The Generic summary scale contained several misfitting items and exhibited multidimensionality. The Cancer-Specific summary scale and Benefits domain showed fit to the Rasch model and demonstrated unidimensionality and no DIF, with just one or no item modifications respectively.
  
  
  CONCLUSIONS
  QLACS demonstrates similarly good classic psychometric properties among shorter-term as among longer-term survivors, and has good feasibility. The Cancer-Specific summary scale and Benefits domain showed an impressive degree of fit to the Rasch model, although the validity of computing the Generic summary score was not supported.
authors.affiliation: School of Social, Psychological and Communication Sciences, Faculty of Health and Social Sciences, Leeds Metropolitan University, Leeds, UK. Electronic address: l.j.ashley@leedsmet.ac.uk.
authors.forename: Laura
authors.initials: L
authors.lastname: Ashley
authors.affiliation: York Health Economics Consortium, University of York, York, UK; Research Innovation Office, University of York, York, UK.
authors.forename: Adam B
authors.initials: AB
authors.lastname: Smith
authors.affiliation: Psychosocial Oncology and Clinical Practice Research Group, Leeds Institute of Cancer and Pathology, Faculty of Medicine and Health, University of Leeds, Leeds, UK.
authors.forename: Helen
authors.initials: H
authors.lastname: Jones
authors.affiliation: Psychosocial Oncology and Clinical Practice Research Group, Leeds Institute of Cancer and Pathology, Faculty of Medicine and Health, University of Leeds, Leeds, UK.
authors.forename: Galina
authors.initials: G
authors.lastname: Velikova
authors.affiliation: Psychosocial Oncology and Clinical Practice Research Group, Leeds Institute of Cancer and Pathology, Faculty of Medicine and Health, University of Leeds, Leeds, UK.
authors.forename: Penny
authors.initials: P
authors.lastname: Wright
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000175:diagnosis; D011594:Psychometrics; D011788:Quality of Life; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires / Q000592:standards*; D017741:Survivors; D013997:Time Factors
keywords: Cancer; Psychometrics; QLACS; Quality of life; Rasch measurement; Survivors