Internal construct validity of the Warwick-Edinburgh Mental Well-being Scale (WEMWBS): a Rasch analysis using data from
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BioMed Central
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Internal construct validity of the Warwick-Edinburgh Mental Well-being Scale (WEMWBS): a Rasch analysis using data from the Scottish Health Education Population Survey Sarah Stewart-Brown*1, Alan Tennant2, Ruth Tennant3, Stephen Platt4, Jane Parkinson5 and Scott Weich1 Address: 1Warwick Medical School, University of Warwick, Coventry, CV4 7AL, UK, 2Department of Rehabilitation Medicine, Faculty of Medicine and Health, The University of Leeds, Leeds General Infirmary, St George St, Leeds, LS1 3EX, UK, 3Coventry Teaching Primary Care Trust, Christchurch House, Greyfriars Lane, Coventry, CV1 2GQ, UK, 4Community Health Sciences, School of Clinical Sciences & Community Health, University of Edinburgh, Teviot Place, Edinburgh, EH8 9AG, UK and 5NHS Health Scotland, Elphinstone House, 65 West Regent Street, Glasgow, G2 2AF, UK Email: Sarah Stewart-Brown* - [email protected]; Alan Tennant - [email protected]; Ruth Tennant - [email protected]; Stephen Platt - [email protected]; Jane Parkinson - [email protected]; Scott Weich - [email protected] * Corresponding author
Published: 19 February 2009 Health and Quality of Life Outcomes 2009, 7:15
doi:10.1186/1477-7525-7-15
Received: 8 September 2008 Accepted: 19 February 2009
This article is available from: http://www.hqlo.com/content/7/1/15 © 2009 Stewart-Brown et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract Background: The Warwick-Edinburgh Mental Well-Being Scale (WEMWBS) was developed to meet demand for instruments to measure mental well-being. It comprises 14 positively phrased Likert-style items and fulfils classic criteria for scale development. We report here the internal construct validity of WEMWBS from the perspective of the Rasch measurement model. Methods: The model was applied to data collected from 779 respondents in Wave 12 (Autumn 2006) of the Scottish Health Education Population Survey. Respondents were aged 16–74 (average 41.9) yrs. Results: Initial fit to model expectations was poor. The items 'I've been feeling good about myself', 'I've been interested in new things' and 'I've been feeling cheerful' all showed significant misfit to model expectations, and were deleted. This led to a marginal improvement in fit to the model. After further analysis, more items were deleted and a strict unidimensional seven item scale (the Short Warwick Edinburgh Mental Well-Being Scale (SWEMWBS)) was resolved. Many items deleted because of misfit with model expectations showed considerable bias for gender. Two retained items also demonstrated bias for gender but, at the scale level, cancelled out. One further retained item 'I've been feeling optimistic about the future' showed bias for age. The correlation between
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