Sleep apnea patients may use CPAP more if they see how they stack up against others

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Eligibility criteria: * The patient has been diagnosed with SAS and has initiated CPAP therapy according to the criteria of Japanese public health insurance system(i.e., Apnea hypopnea index (AHI) \>= 20/h by polysomnography, or respiratory event index (REI) is \>= 40/h by portable monitoring device at the time of OSA diagnosis). * The patient makes regular outpatient visits for the continuation of CPAP therapy according to the requirements for the coverage of Japanese public health insurance. * At least three months have passed since the introduction of a CPAP remote monitoring system, and the researchers can confirm CPAP adherence online. * The patient has mailing address necessary for sending feedback by post or email. Exclusion Criteria: * Treatment adherence is already sufficiently good, with little need for further improvement. (Defined as a proportion of days with \>4 hours of CPAP use of 90% or higher, and an average daily usage time \>=7 hours over the past month.) * No CPAP usage at all during the past month (for example, due to business trips, caring for family members, or other social reasons resulting in an inability to use CPAP, and for whom improvement in adherence through this intervention is not expected). * Working night shifts twice or more a week. * Patients with cognitive impairment Intervention Details 1. When a patient who is a potential participant visits the outpatient clinic for continued CPAP therapy, their CPAP adherence during the previous month will be checked. 2. If the patient's background and CPAP adherence over the previous month meet the inclusion criteria, informed consent will be obtained from the patient. 3. After the number of patients who have provided consent reaches the planned sample size, a postal item will be sent to confirm the accuracy of the participant's address. The mailing will include a postcard for reply or QR code that allows the research team to verify that the participant has received the item. Participants whose receipt of the mailing can be confirmed will be eligible for randomization. 4. Participants will be randomly assigned to either the control group (receiving only information about their own CPAP adherence) or the peer comparison group (receiving information about their own adherence plus the summary of adherence data from all participants). 5. Thereafter, for six months, participants will receive by mail monthly information about their CPAP adherence. Each mailing will include a postcard for reply and a QR code that allow participants to notify the researchers that they have opened the mailing. In the control group, the following information will be provided:(1) Average daily CPAP usage time in the previous month, and (2) Percentage of days with CPAP usage more than or equal to 4 hours per day.In the peer comparison group, in addition to the above, the following information will be provided: (3) Mean daily CPAP usage time among all participants, (4) Percentage of days with CPAP usage ≥ 4 hours per day among all participants, and (5) Participant's rank among all participants based on average daily CPAP usage time.