Table 1.

Selection criteria.

Category	Inclusion criteria	Exclusion criteria
Population	Young people aged 14-24 years Young people aged 14-24 years and additionally 1 year either side of this range (eg, young people aged 13-16 years would be included, whereas those aged 16-26 years would be excluded)	Nonhuman subjects Adults aged ≥25 years if unable to easily separate results from those of younger group
Intervention	Explores QSCa (ie, mentions relevant attributes such as empathy, feeling listened to, understood by another person) Use of a digital intervention, software, or internet-delivered services (eg, smartphone app, virtual reality packages, internet-based treatment, and chat room)	No mention of QSC (eg, focuses only on quantity of connections) No mention of digital intervention (eg, based on a face-to-face situation only)
Comparator	N/Ab	N/A
Outcome	Scope of depression and anxiety spanned all forms, including major, bipolar, psychotic, perinatal, postpartum, PMDDc, and manic depression, as well as social, generalized, OCDd, panic, PTSDe, and anxiety disorders Influence on existing symptoms of depression or anxiety (eg, mood and self-esteem through self-report questionnaire or clinical interview) Prevention of onset of depression or anxiety (eg, measuring mental well-being through self-report questionnaire or clinical interview)	No mention of depression or anxiety No mention of the influence on existing symptoms of depression or anxiety No mention of the influence on depression or anxiety prevention
Study design	All study designs	N/A
Dates	From earliest date to June 24, 2020	Outside date remit

^aQSC: quality social connection.

^bN/A: not applicable.

^cPMDD: premenstrual dysphoric disorder.

^dOCD: obsessive-compulsive disorder.

^ePTSD: posttraumatic stress disorder.