The sleep quality category was defined by grouping the ‘sleep well’ factor from the WURSS-21 questionnaire (Q13) and the ‘snoring’ factor from the additional QoL questions (Q1). The severity scale for sleep quality was calculated by adding the two individual QoL scores included; the resulting range was 0–14, where 14 represented the highest severity. Because the ‘snoring’ factor could only be measured in participants who lived with a partner, the analyses for sleep quality category were assessed on an initial n of 80 participants, and not on the full mITT population (n = 102).