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Interpretation of change scores for the National Eye Institute Visual Function Questionnaire-25: the minimally important difference
  1. Jennifer M Burr1,
  2. David Cooper2,
  3. Craig R Ramsay2,
  4. Jemaima Che Hamzah3,
  5. Augusto Azuara-Blanco4
  1. 1School of Medicine, University of St Andrews, St Andrews, UK
  2. 2Health Services Research Unit, University of Aberdeen College of Life Sciences and Medicine, Aberdeen, Aberdeen, UK
  3. 3Department of Ophthalmology, Universiti Kebangsaan Malaysia, Kuala Lumpur, Cheras, Malaysia
  4. 4Centre for Public Health, Queen's University Belfast, Belfast, Northern Ireland, UK
  1. Correspondence to Dr Jennifer M Burr, University of St Andrews, St Andrews KY16 9AJ, UK; jmb28{at}st-andrews.ac.uk

Abstract

Aim To estimate the minimally important difference (MID) in change in National Eye Institute Visual Function Questionnaire-25 (VFQ-25) composite score using methods aligned with patient perception.

Methods Retrospective analysis of prospectively collected data from adults with primary angle closure or primary angle closure glaucoma enrolled in the Effectiveness, in Angle-closure Glaucoma, of Lens Extraction study. We included data from 335 participants with patient reported visual function (VFQ-25) and health status measured by the EQ-5D-3L over 36 months. We used the recommended anchor-based methods (receiver operating characteristic (ROC), predictive modelling and mean change) to determine the MID of the VFQ-25. EQ-5D-3L anchor change was defined as none (<0.065); minimal (0.065≤EQ-5D-3L change ≤0.075 points) and greater change (>0.075 points).

Results Mean baseline VFQ-25 score was 87.6 (SD 11.8). Estimated MIDs in the change in VFQ-25 scores (95% CI) were 10.5 (1.9 to 19.2); 3.9 (−2.3 to 10.1); 5.8 (1.9 to 7.2) and 8.1 (1.7 to 14.8) for the ‘within-patient’, ‘between-patient’ change, ROC and predictive modelling anchor methods respectively. Excluding estimates from the methodologically weaker ‘within-patient’ method, the MID of a change in VFQ-25 composite score is 5.8 (median value).

Conclusions Estimates of the MID using multiple methods assist in the interpretation of the VFQ scores. In the context of early glaucoma related visual disability, a change score of around six points on the VFQ-25 is likely to be important to patients. Further confirmatory research is required. Studies comparing changes in patient-reported outcome measure scores with a global measure of patients’ perceived change are required.

  • glaucoma
  • epidemiology

Data availability statement

Data are available on reasonable request.

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Data availability statement

Data are available on reasonable request.

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Footnotes

  • Contributors JMB, DC and CRR conceived and designed the study, DC undertook the statistical analysis. All authors contributed to the drafting of the manuscript and approved the final version.

  • Funding The EAGLE trial was supported by the Medical Research Council (MRC G0701604) on behalf of the MRC NIHR partnership. The Health Services Research Unit is core funded by the Chief Scientist Office of the Scottish Government Health and Social Care Directorates (award number: not applicable).

  • Disclaimer The view and opinions expressed in this study are those of the authors and do not necessarily reflect those of the funder.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.

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