2.1. Participants

We recruited participants from 10 January to 20 December 2018, via advertising on a university campus in Japan. A total of 175 students completed the informed consent form and online questionnaires. Inclusion criteria included: (1) university students, and (2) a total Insomnia Severity Index (ISI) score ≥ 10, a clinical cut-off point to distinguish insomniac patients from normal sleepers for the Japanese version of the ISI [18]. Exclusion criteria included: (1) ISI score < 10, and (2) a current or past medical history of mental disorder, such as bipolar or schizophrenia spectrum disorder. After exclusions, the remaining 48 participants (67% female, 19.56 (SD = 1.86)) were randomly assigned to either the REFRESH group (8 males, 16 females, n = 24) or to a self-monitoring group (SM) that recorded their sleep diaries (8 males, 16 females, n = 24) for 8 weeks (Figure 1).

Study flowchart.