The Visual Analogue WOMAC 3.0 scale - internal validity and responsiveness of the VAS version

BMC Musculoskeletal Disorders

Research Article

Alan Tennant¹  Paula Kersten²  Peter J White² 

[1] Department of Rehabilitation Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, UK;School of Health Sciences, University of Southampton, Highfield, Southampton, UK;

关键词: Differential Item Functioning;    Ordinal Data;    Standardise Response Means;    Visual Analogue Scale Scale;    Person Separation Index;   

DOI  :  10.1186/1471-2474-11-80

 received in 2010-01-13, accepted in 2010-04-30,  发布年份 2010

来源: Springer

【 摘 要 】

BackgroundMany people suffer with Osteoarthritis (OA) and subsequent morbidity. Therefore, measuring outcome associated with OA is important. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) has been a widely used patient reported outcome in OA. However, there is relatively little evidence to support the use of the Visual Analogue Scale (VAS) version of the scale. We aimed to explore the internal validity and responsiveness of this VAS version of the WOMAC.MethodsPatients with chronic hip or knee pain of mechanical origin, waiting for a hip or knee joint replacement completed the WOMAC as part of a study to investigate the effects of acupuncture and placebo controls. Validity was tested using factor analysis and Rasch analysis, and responsiveness using standardised response means.ResultsTwo hundred and twenty one patients (mean age 66.8, SD 8.29, 58% female) were recruited. Factor and Rasch analysis confirmed unidimensional Pain and Physical Functioning scales, capable of transformation to interval scaling and invariant over time. Some Differential Item Functioning (DIF) was observed, but this cancelled out at the test level. The Stiffness scale fitted the Rasch model but adjustments for DIF could not be made due to the shortness of the scale. Using the interval transformed data, Standardised Response Means were smaller than when using the raw, ordinal data.ConclusionsThe WOMAC Pain and Physical Functioning subscales satisfied unidimensionality and ordinal scaling tests, and the ability to transform to an interval scale. Some Differential Item Functioning was observed, but this cancelled out at the test level and, by doing so, at the same time removed the disturbance of unidimensionality. The scaling characteristics of sets of items which use VAS require further analysis, as it would appear that they can lead to spurious levels of responsiveness and scale compression because they exaggerate the distortion of the ordinal scale.Trial numberUKCRN study ID: 4881ISRCTN78434638

【 授权许可】

CC BY   
© Kersten et al; licensee BioMed Central Ltd. 2010