Within-person variability and the minimal important difference of the EQ-VAS in adults with post-COVID-19 condition: a secondary analysis of data from a single-centre randomised controlled trial
In brief
Researchers estimate an 8-point meaningful change on long COVID health ratings
In 153 adults with post-COVID-19 condition, researchers estimated that an 8-point change on the 0-to-100 health rating scale represents a meaningful difference. Ratings varied considerably from day to day, supporting weekly averages over single-day scores; the estimate comes from a fatigue-predominant group, so its relevance to other people with long COVID remains uncertain.
- Journal
- BMJ open (Q1)
- Published
- 25 September 2026
- Study design
- Randomized controlled trial
- Evidence level
- Level 1, High (CEBM 1b)
- Authors
- Julia Kopp, Tala Ballouz, Dominik Menges, Anja Frei, Julia Braun, Lisa Kuenzi, et al.
- PMID
- 42790915
- DOI
- 10.1136/bmjopen-2026-121051
Why clinicians should know about it
- Picked for Internal Medicine (top studies of the week, 27 September 2026): Ranked by evidence level and journal quartile
Abstract
OBJECTIVE: To describe the distribution and day-to-day variability of EuroQol Visual Analogue Scale (EQ-VAS) values and to estimate a minimal important difference (MID) in adults with post-COVID-19 condition (PCC). DESIGN: Secondary analysis of pooled EQ-VAS data from both arms of a 12-week randomised, placebo-controlled trial (PYCNOVID) of Pycnogenol (200 mg/day) versus placebo in adults with PCC. SETTING: Single centre study in Switzerland between June 2023 and July 2024. PARTICIPANTS: Adults with PCC with at least one of the following symptoms: fatigue, post-exertional malaise, dyspnoea or brain fog. MAIN OUTCOME MEASURE: EQ-VAS ratings over 7 consecutive days before baseline (randomisation) and at follow-up (after 12 weeks). Weekly mean EQ-VAS values and within-person SDs (wpSD) were calculated. The MID was estimated using distribution-based and anchor-based methods with prespecified correlation criteria, using the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-Fatigue) instrument as the primary anchor, along with additional anchors. RESULTS: Among 153 participants, baseline EQ-VAS values were low, with a median of 48.7 on a 0-100 scale. Day-to-day variability was considerable, with a median wpSD of 6.4. Distribution-based MID estimates ranged from 5.9 to 8.9 points. FACIT-Fatigue was the only anchor meeting the correlation threshold (ρ≥0.30), yielding an anchor-based MID of 8.96 points. Triangulation of these estimates supported a final MID estimate of 8 EQ-VAS points. CONCLUSIONS: Adults with PCC reported markedly impaired and highly variable health status. Weekly aggregation of daily EQ-VAS ratings likely provides a more robust estimate than single-day assessments. A PCC-specific EQ-VAS MID of 8 points, derived from a chronic, fatigue-predominant PCC population, facilitates interpretation of meaningful change and improves outcome definition and sample size planning in future studies. Applicability to earlier-stage or non-fatigue-predominant PCC populations warrants further investigation. TRIAL REGISTRATION NUMBER: NCT05890534.
Abstract as published, via PubMed.
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