Health State Values Should Not Be Used as Minimal Important Differences

This article critically examines the application of minimal important differences (MIDs) to health state values or utilities. The concept of MIDs aims to guide clinical and research decisions by identifying important changes in health-related quality-of-life (HRQoL) indicators. However, this cannot be used without additional information not contained within the indicator itself, so that the MID cannot be regarded as a property of the indicator. First, MIDs defined at the individual patient level cannot be meaningfully aggregated for groups without additional context. Second, any improvement in HRQoL is important for patients themselves, so decision making using an MID also requires context, such as resource costs for effecting change. Third, health state values incorporate a measure of importance according to patient preferences, so the only change that is unimportant is zero. Calculating and reporting MIDs for health state values is not only unhelpful but also misleading. Highlights The minimal important difference (MID) for health-related quality of life and patient-reported outcome measures is widely used but arguably is not only of limited use but also usually misleading because it lacks context-specific meaning. MIDs for individuals cannot be aggregated without judgments about the distribution of outcomes over patient groups, and quality-of-life indicators need context; thus, the MID cannot be regarded as a property of an indicator. Quality-of-life indicators that generate health state values or utilities incorporate importance based on patient preferences, so the only unimportant change is zero. Published research into MIDs for health state values is unhelpful and even misleading.