title: Validation of the Questionnaire to Identify Knee Symptoms (QuIKS) using Rasch analysis.
abstract: BACKGROUND
  The Questionnaire to Identify Knee Symptoms (QuIKS) was recently developed to promote activity by screening for experiences related to early symptoms in people with emergent chronic knee pain problems, such as osteoarthritis (OA) - like knee pain. The main purpose of the current study was to evaluate measurement properties of the QuIKS using Rasch analysis in a sample of people with knee symptoms consistent with symptomatic knee OA.
  
  
  METHODS
  This study used cross-sectional data. The sample was 200 subjects along the following knee health continuum: pain-free healthy knees (n = 55) from a university community, knee pain with no knee OA diagnosis (n = 111) from a university-affiliated medical clinic, and patients with surgeon-diagnosed symptomatic knee OA awaiting high tibial osteotomy (n = 34) from a sports medicine surgical clinic. The 13-item QuIKS was evaluated for its factor structure, item- and person-fit, item's category response structure, differential item functioning by sex and obesity status, local item dependency, unidimensionality, and test precision. Subsequently, the QuIKS underwent known-groups analysis and convergent validity with the Knee injury and Osteoarthritis Outcome Score (KOOS).
  
  
  RESULTS
  In the QuIKS, each item's category response structure was modified. No differential item functioning was observed. Local item dependency informed the formation of four testlets. This refined QuIKS obtained summary fit to the Rasch measurement model, unidimensionality, reliability (person separation index = 0.82), and interval-level scoring. Subsequently, the Rasch-validated QuIKS (QuIKS-R) demonstrated excellent known-groups validity and good convergent validity with the KOOS (Spearman's rho = 0.45 to 0.77).
  
  
  CONCLUSIONS
  The QuIKS-R provides interval-level quantification of knee symptoms-related experiences in people with knee symptoms consistent with symptomatic knee OA. Its scores might be useful for clinicians for promoting activity in individuals with early symptoms consistent with symptomatic knee OA.
authors.affiliation: Graduate Program in Health and Rehabilitation Sciences, Western University, London, ON, Canada. chamil7@uwo.ca.
authors.forename: Clayon B
authors.initials: CB
authors.lastname: Hamilton
authors.affiliation: Institute for Applied Health Sciences, McMaster University, Hamilton, ON, Canada. mmaly@mcmaster.ca.
authors.forename: Monica R
authors.initials: MR
authors.lastname: Maly
authors.affiliation: Department of Surgery, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada. rgiffin@uwo.ca.
authors.forename: J Robert
authors.initials: JR
authors.lastname: Giffin
authors.affiliation: Department of Surgery, University of Alberta, Edmonton, AB, Canada. Jmclark@ualberta.ca.
authors.forename: Jessica M
authors.initials: JM
authors.lastname: Clark
authors.affiliation: Department of Epidemiology and Biostatistics, Schulich School of Medicine & Dentistry; Schulich Interfaculty Program in Public Health, Western University, London, ON, Canada. mark.speechley@schulich.uwo.ca.
authors.forename: Mark
authors.initials: M
authors.lastname: Speechley
authors.affiliation: Department of Family Medicine, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada. petrella@uwo.ca.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Petrella
authors.affiliation: School of Physical Therapy and Department of Epidemiology and Biostatistics, Schulich School of Medicine & Dentistry, Western University, London, ON, N6G1H1, Canada. bcheswor@uwo.ca.
authors.forename: Bert M
authors.initials: BM
authors.lastname: Chesworth
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D003430:Cross-Sectional Studies; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D007718:Knee Injuries / Q000175:diagnosis* / Q000534:rehabilitation; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000175:diagnosis* / Q000534:rehabilitation; D011594:Psychometrics; D011788:Quality of Life; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires / Q000592:standards*