Responses to selected questions from the Sleep & Health Questionnaire.

The responses to the questionnaire utilized either a 5-point frequency scale ("never", "rarely", "sometimes", "frequently" and "almost always"); or by the use of a 6—point Likert scale which graded the severity of the symptoms. The responses were categorized into mild, moderate and severe as follows for the purpose of data analysis18,29,30:
6-point Likert scale: 1–2 points (not affected); 3–4 points (mild); 5 points (moderate); 6 points (severe)
5-point frequency scale: never (not affected); rarely or < once/week(mild); sometimes or 1–2/week (mild); frequently or 3–4/week(moderate); almost always or 5–7/week (severe)
Responses to snoring intensity:
0 (not affected); 1–2 points (mild); 3 points (moderate); 4 points (severe)
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