Table 2. Search criteria.

	Exclusion criteria	Inclusion criteria
Manuscript characteristics	• Interventional studies • studies not in English language • Studies not published by a peer-reviewed scientific journal, conference abstracts and proceedings, unpublished data, preprints, government publications, scientific or case reports, dissertations, and theses, review articles and follow-up studies • Guidelines, statements, and comments • No measurement of the SOP • No reliable and scientifically valid methods of sleep measurements	• Original and peer reviewed research articles • Observational, descriptive, longitudinal, retrospective, cross-sectional, cohort, studies that investigate SOP • Methodologies and samples were well-described (e.g., scoring criteria, modality and measurement of the exact point of SO)
Population’s characteristics	• Participants under 18, infants, paediatric	• Healthy controls >18 years of age
	• Animal studies	• Individuals with sleep disorders
		• Diagnoses made in accordance with DSM-IV, clinical review and laboratory examinations to rule out other medical and psychiatric disorders [Spitzer et al., 1992 (42)]
Study design	RCT; CCT	Appropriate and clinically valid designs to measure the SOP

SO, sleep-onset; SOP, sleep-onset period; RCT, randomized controlled trial; CCT, controlled clinical trial.