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Quality of Life Research

, Volume 21, Issue 2, pp 237–246 | Cite as

The validity of subjective quality of life measures in psychotic patients with severe psychopathology and cognitive deficits: an item response model analysis

  • Ulrich Reininghaus
  • Rosemarie McCabe
  • Tom Burns
  • Tim Croudace
  • Stefan Priebe
Article

Abstract

Purpose

Subjective quality of life (SQOL) is an established patient-reported outcome in the evaluation of treatments for psychosis. The use of SQOL measures in the presence of psychiatric symptoms and cognitive deficits has been questioned. However, there is little evidence on whether items function differently as indicators of SQOL in psychotic patients with different levels of symptoms and deficits. Substantial differential item functioning (DIF) would, indeed, challenge the validity of established measures. We aimed to investigate the validity of a widely used measure of subjective quality of life (SQOL), i.e., the Lancashire Quality of Life Profile (LQOLP), in the presence of cognitive deficits and psychiatric symptoms in patients with severe and enduring psychosis.

Method

We analysed SQOL ratings of 690 psychotic patients on the LQOLP using item response modelling to detect differential item functioning (DIF) attributable to psychiatric symptoms and cognitive deficits.

Results

Patients with more severe general psychopathology were less likely to rate their ‘personal safety’ positively (OR .96, 95% CI .93–.99). More severely depressed patients were less likely to endorse positive ‘life as a whole’ (OR .93, 95% CI .89–.98) and ‘mental health’ (OR .93, 95% CI .91–.97) ratings. There was no DIF attributable to cognitive deficits.

Conclusions

The findings suggest that the validity of the LQOLP in psychotic patients may be impaired by DIF due to psychopathology, although the magnitude of effects is unlikely to be of clinical significance. The validity appears not to be compromised by cognitive deficits.

Keywords

Quality of life Patient-reported outcomes Psychosis Validity Differential item functioning Item response theory 

Notes

Acknowledgments

This work was supported by a Research Training Fellowship funded by the National Institute of Health Research, UK, to U.R. The report is independent research and the views expressed in this publication are those of the authors and not necessarily those of the NHS, the National Institute for Health Research or the Department of Health.

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Copyright information

© Springer Science+Business Media B.V. 2011

Authors and Affiliations

  • Ulrich Reininghaus
    • 1
    • 2
  • Rosemarie McCabe
    • 1
  • Tom Burns
    • 3
  • Tim Croudace
    • 4
  • Stefan Priebe
    • 1
  1. 1.Unit for Social and Community Psychiatry, Barts and the London School of Medicine, Newham Centre for Mental HealthQueen Mary University of LondonLondonUK
  2. 2.Department of PsychiatryUniversity of CambridgeCambridgeUK
  3. 3.Department of PsychiatryUniversity of Oxford, Warneford HospitalOxfordUK
  4. 4.Department of PsychiatryUniversity of Cambridge, Addenbrooke’s HospitalCambridgeUK

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