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Exploring the applicability of the minimally important difference concept in interpreting generic indirect preference-based health-related quality of life outcomes
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- Author / Creator
- McClure, Nathan S
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Generic indirect preference-based measures of health-related quality of life (HRQL), such as the EQ-5D-5L index score, were developed to assign health preference weights to time lived in different health states in order to calculate quality-adjusted life years (QALYs), a common outcome measure for economic evaluations. A key feature of the index score like the EQ-5D-5L is the anchoring of the scale at 1.0 for full health and 0.0 for dead. Since everyone is a potential patient whose condition and treatment needs are uncertain, it is recommended that preference weights reflect the average of the general population’s health preferences. However, this masks underlying preference heterogeneity, which presents a challenge for end-users of generic HRQL instruments who seek to understand whether patients’ HRQL has improved or worsened over time. Thus, the concept of the minimally important difference (MID), defined as the smallest change in EQ-5D-5L index score that can be expected to reflect minimally important improvement or deterioration in patients’ HRQL, may be a useful way of interpreting observed index score changes.
Plausible MID estimates for EQ-5D-5L index scores range from 0.037 to 0.069 depending on the country-specific scoring algorithm and baseline score. For patients with type 2 diabetes, as an example of a chronic condition in the general population, MID estimates for index scores based on multiple approaches ranged from 0.03 to 0.05, and were further found to vary by direction of change. Secondary analysis of responses from the Canadian Valuation Study showed how the variability in individual-level interpretation of (small) index score differences resulted in a health state transition having to be ‘large enough’ (i.e., > +/- 0.05 change in index score) to be meaningfully interpretable as an improvement or deterioration in HRQL. Based on evidence of MIDs, a new method for calculating QALYs was proposed adjusting for meaningful within-patient change in HRQL. Comparing incremental QALY estimates using different methods in a case study for depression treatment in patients with type 2 diabetes showed how the method of QALY calculation and adjustment for between-group differences yields different results (ranging from -0.028 to 0.031). The uncertainty in incremental QALY estimates reflects uncertainty in regards to the value of small EQ-5D-5L index score changes.
This research found MID estimates that reflect greater than zero change in EQ-5D-5L index score, suggesting that observed index score changes smaller than the MID do not adequately represent HRQL improvement or deterioration from the patients’ perspective. Therefore, the MID may be useful in determining whether or not the observed index score change is expected to represent meaningful change in patients’ HRQL. In doing so, there is an explicit incorporation of patients’ HRQL in the interpretation of HRQL outcomes from generic indirect preference-based measures.
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- Graduation date
- Fall 2020
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.