Minimal important differences to assess cross-sectional differences among groups and minimal important changes to assess longitudinal within-patient changes for the Mayo Clinic Vestibular Schwannoma Quality of Life Index.

OBJECTIVE

The minimal important difference (MID) and minimal important change (MIC) are two metrics that bridge the gap between statistical significance and clinical relevance and are critical to managing clinical decisions and conducting clinical research. The objective of this study was to define MIDs to evaluate cross-sectional differences among groups and to define MICs to evaluate longitudinal within-patient changes for the Mayo Clinic Vestibular Schwannoma Quality of Life (VSQOL) Index.

METHODS

Anchor-based methods were used to define MIDs and MICs for the VSQOL Index domain scores, which range from 0 to 100 points, for a national cohort of 1050 patients with sporadic vestibular schwannoma, 644 of whom completed the VSQOL Index twice approximately 1 year apart.

RESULTS

The median of the MID estimates for the VSQOL Index domains were: hearing problems (17, IQR 12.5-21); dizziness and imbalance (21, IQR 18-23); pain, discomfort, and tinnitus (19.5, IQR 15-23.5); problems with face or eyes (18, IQR 17-28); impact on physical, emotional, and social well-being (19.5, IQR 14.5-23.5); difficulty with thinking and memory (23.5, IQR 18.5-28.5); global quality of life (12, IQR 8-16); and satisfaction or regret (13.5, IQR 7-17). MIC estimates for the hearing problems and satisfaction and regret domains were not obtained because the correlations between these domain scores and their associated anchors were not sufficiently strong. The MIC estimates (minimum and maximum) for the remaining domains were: dizziness and imbalance (7.2 and 8.3); pain, discomfort, and tinnitus (8.3 and 8.5); problems with face or eyes (7.0 and 7.4); impact on physical, emotional, and social well-being (2.1 and 8.0); and difficulty with thinking and memory (12.9 and 15.0). The median of the MIC estimates for global quality of life was 5.2 (IQR 3.7-5.6).

CONCLUSIONS

The MIDs and MICs reported herein provide a framework to interpret quality-of-life benefit or harm cross-sectionally among groups and longitudinally within patients. Moving forward, these values should be considered when interpreting studies using the VSQOL Index to assess disease-specific quality of life in patients with sporadic vestibular schwannoma.