Efficacy of Mobile-delivered Sleep Restriction Therapy for Treatment of Insomnia Disorder: Randomised Controlled Trial

Insomnia Severity Index (ISI) is a 7-item questionnaire used to examine overall insomnia severity. It consists of a five-point Likert type scale for each item (ranging from "no problem" = 0 to "severe problem" = 28) regarding symptoms over the past 2 weeks. Scores range from 0-28 with higher scores indicating greater insomnia symptom severity.

Sleep- wake metrics will be determined from the Pittsburgh Sleep Quality Index Score (PSQI) - a 19-item questionnaire with seven component scores derived from the responses, each scored 0 (no difficulty) to 3 (severe difficulty). The component scores are summed to produce a global score (range 0-21) where a score of 5 or more indicates poor sleep quality.

The Flinders Fatigue Scale (FFS) is a 7-item self-reported instrument designed to measure the level of subjective daytime fatigue experienced over the previous two weeks. 6-items consist of a 5-point Likert type scale ranging from "not at all" = 0 to "extremely" = 4. Item 5 uses a multiple-item checklist and is scored as a sum. All items are summed with total scores ranging from 0-31 with higher scores reflecting greater fatigue.

The General Anxiety Disorder-7 (GAD-7) is a 7-item self-administered scale used to assess the severity of generalised anxiety over the previous 2 weeks. It consists of a three-point Likert type scale for each item (ranging from "not at all" = 0 to "nearly every day" = 3). All items are summed with total scores ranging from 0-21 where 5, 10 and 15 indicate the cut-off scores for mild, moderate and severe anxiety, respectively.

The Patient Health Questionnaire-8 is an 8-item self-reported measure of depressive symptoms over the past 2 weeks. Scores are rated as normal (0-2), mild (3-5), moderate (6-8), and severe (9-12). Total score ≥3 for first 2 questions suggests anxiety. Total score ≥3 for last 2 questions suggests depression.

The EuroQol five-dimensional (EQ-5D) is a self-reported questionnaire which assesses 5 dimensions of mobility, self-care, usual activities, pain/discomfort and anxiety/depression and overall health. The 5 dimensions range from "1 = indicating no problem" - "5 = indicating unable to/extreme problems" and the overall score from 0 (worst health state imaginable) to 100 (best health state imaginable).

The System Usability Scale (SUS) questionnaire is a 10-item survey that examines four dimensions of usability: useful- ness, ease of use, ease of learning, and satisfaction. It is scored out of a 100; scores closer to 100 means excellent usability while scores closer to 0 means worse usability.

Participants will be asked short yes/no questions regarding the use of sleep medication in the previous two weeks.

Participants will be asked short yes/no questions regarding taking sick leaves in the previous two weeks.