An item response theory analysis of an item pool for the recovering quality of life (ReQoL) measure
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An item response theory analysis of an item pool for the recovering quality of life (ReQoL) measure Anju Devianee Keetharuth1 · Jakob Bue Bjorner2 · Michael Barkham3 · John Browne4 · Tim Croudace5 · John Brazier1 Accepted: 20 August 2020 © The Author(s) 2020
Abstract Purpose ReQoL-10 and ReQoL-20 have been developed for use as outcome measures with individuals aged 16 and over, experiencing mental health difficulties. This paper reports modelling results from the item response theory (IRT) analyses that were used for item reduction. Methods From several stages of preparatory work including focus groups and a previous psychometric survey, a pool of items was developed. After confirming that the ReQoL item pool was sufficiently unidimensional for scoring, IRT model parameters were estimated using Samejima’s Graded Response Model (GRM). All 39 mental health items were evaluated with respect to item fit and differential item function regarding age, gender, ethnicity, and diagnosis. Scales were evaluated regarding overall measurement precision and known-groups validity (by care setting type and self-rating of overall mental health). Results The study recruited 4266 participants with a wide range of mental health diagnoses from multiple settings. The IRT parameters demonstrated excellent coverage of the latent construct with the centres of item information functions ranging from − 0.98 to 0.21 and with discrimination slope parameters from 1.4 to 3.6. We identified only two poorly fitting items and no evidence of differential item functioning of concern. Scales showed excellent measurement precision and knowngroups validity. Conclusion The results from the IRT analyses confirm the robust structure properties and internal construct validity of the ReQoL instruments. The strong psychometric evidence generated guided item selection for the final versions of the ReQoL measures. Keywords Mental health · Recovering quality of life · Psychometrics · Item response theory
Background Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11136-020-02622-2) contains supplementary material, which is available to authorized users. * Anju Devianee Keetharuth [email protected] 1
School of Health and Related Research, University of Sheffield, Sheffield, UK
2
Optum Patient Insights, Rhode Island, United States and University of Copenhagen, Copenhagen, Denmark
3
Department of Psychology, University of Sheffield, Sheffield, UK
4
School of Public Health, University College Cork, Cork, Ireland
5
School of Health Sciences, University of Dundee, Dundee, UK
While there are patient-reported outcome measures (PROMs) focusing on the process of recovery from mental health problems [1], a review identified the need for a PROM that measures the outcomes of recovery in terms of those aspects of quality of life that matter to mental health service users [2]. We use the term service users as it is commonplace in the UK to refer to patients experiencing mental heal
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