Interpreting patient-reported outcomes after ischemic stroke: defining minimal important difference in EQ-5D across recovery phases

The EQ‑5D is widely applied to measure patient-reported outcomes, yet its minimally important difference (MID) has not been clearly established across distinct recovery phases after stroke. This study aimed to determine phase‑specific MIDs in EQ‑5D following stroke and to explore heterogeneity by estimation method, direction of change, and stroke etiology. A total of 9978 adults with neuroimaging‑confirmed acute ischemic stroke were included in a prospective longitudinal cohort study. EQ‑5D and modified Rankin Scale (mRS) scores were recorded at admission (V1), hospital discharge (V2), 3-month (V3), and 1-year since admission (V4). Anchor-based MIDs were estimated at both group and individual levels and triangulated by distribution-based and instrument-defined approaches. Changes during the recovery phases (V1–V2, V2–V3, and V3–V4) were grouped into 3 categories: improved, no change, and deteriorated. Subgroup analyses were conducted according to the TOAST classification. Credibility of MID estimates was assessed using a validated instrument for anchor-based methods. Phase-specific group-level MIDs for improvement decreased over time: anchor-based estimates were 0.19 at V2, 0.14 at V3, and 0.11 at V4, while deterioration MIDs were smaller. Distribution-based and instrument-defined estimates fluctuated slightly around the anchor-based values but followed a similar downward trend over time. Individual‑level analyses yielded MIDs with acceptable discriminative power (area under the curve ≥ 0.70) only for improvement at V2 (0.10) and V3 (0.01). Cardioembolic strokes had higher MIDs than large-artery atherosclerosis and small-artery occlusion, while baseline utilities showed the reverse. Credibility assessment confirmed high reliability. This study provides the phase‑specific MIDs for utility measures after ischemic stroke, showing a declining trend from acute to chronic recovery and confirming robustness across multiple estimation methods. While group‑level MID ranges are recommended for effect size interpretation, trial design, and evidence certainty rating, individual‑level thresholds should be reserved for personalized evaluation. These values assist in the interpretation of patient‑reported outcome changes and evaluation of healthcare interventions across different recovery phases. ClinicalTrials.gov NCT02470624. Registered 10 June 2015.