Minimum clinically important difference of the Epworth Sleepiness Scale

Background: The Epworth Sleepiness Scale (ESS) is a self-administered questionnaire used to quantify daytime sleepiness (ESS 0–24) with higher scores indicating increased daytime hypersomnolence. The minimum clinically important difference (MCID) of the ESS is unknown. Aims: To determine the MCID of the ESS in patients with obstructive sleep apnoea, started on continuous positive airway pressure (CPAP) therapy. Methods: ESS was measured at baseline and follow-up (3 months post CPAP initiation). At follow-up, participants were asked to complete a seven-point Likert global rating of change (GROC) in sleepiness questionnaire, ranging from “1: Much less sleepy” to “7: Much more sleepy”. The MCID of the ESS was estimated using anchor-based methods (mean change in ESS and Receiver Operating Characteristic curves for those scoring “3: Slightly less sleepy” in GROC). Results: 99 CPAP users returned for follow-up. Baseline characteristics: 66 men (67%); mean±SD: age 55±12years; BMI 33.8±7.5kg/m2; ESS 12.7±5.3. Self-reported CPAP compliance was 4.5±2.8hours. With CPAP, mean(95% CI) change in ESS was -4.5(-5.6 to -3.5). Mean±SD change in ESS for those slightly less sleepy was -2.5±2.1 (Fig 1); an ESS change of -2 had an area under curve of 0.93, sensitivity 91% and specificity 88% in identifying those who scored at least feeling “slightly less sleepy”. Conclusion: Using anchor-based methods, the MCID (for improvement) of the ESS lies between -2 and -3.