Table 2.

Frequencies of countries, ecological systems, age groups, and study designs across the selected studies reviewed (N = 39).

	Reference Numbers	No. of Studies
United States	[5,6,51,52,53,54,55,56,57,58,59,60,61]	13
China	[62,63,64,65]	4
Canada	[66,67,68]	3
Portugal	[69,70,71]	3
Europe a	[7,38,39]	3
New Zealand	[72,73]	2
Finland	[9,74]	2
Australia	[8,75]	2
Germany	[76]	1
Brazil	[77]	1
Estonia	[78]	1
Norway	[79]	1
Spain	[80]	1
Vietnam	[81]	1
United Kingdom	[82]	1
Microsystem	[5,6,8,9,38,51,52,53,54,55,56,57,58,59,60,61,63,64,65,66,67,68,69,70,71,73,74,75,76,77,78,79,81,82]	34
Individual	[8,54,56,57,58,59,60,61,62,63,67,68,69,73,74,75,76,79,80,81]	20
Macrosystem	[7,38,39,59,61,63,72,73,76]	9
Exosystem	[59,61,73,81]	4
Chronosystem	[67]	1
Children b	[5,6,8,9,38,51,53,61,62,66,68,70,71,72,76,78,79,82]	18
Adolescents	[7,39,52,54,55,56,58,59,60], [64] c, [65,69,73,74,77,80]	16
Mixed children and adolescents	[57] (10–16 years.), [63] (11–17 years.), [67] (9–13 years.), [75] (11–13 years.), [81] (11–16 years.)	5
Cross-sectional d	[6,7,8,9,38,39,51,52,55,58,59,61,62,63,66,68,69,70,71,72,73,76,77,78,80,81,82]	27
Longitudinal e	[5,53,57,60,64,67,74,75]	8
RCTs f	[65,79]	2
Cohort sequential	[54]	1
Mixed method	[56]	1

Note: ^a Europe included 7, 29, and 34 countries in three studies [7,38,39], respectively (see Supplementary Materials File C). ^b According to [3,40], children is defined as 3–12 years old. Adolescent is defined as 12–18 years old. Mixed indicated participants’ age ranging from 3–18 years old. ^c Study [78] included 11-year longitudinal data through adolescence to young adulthood. ^d [71] applied cross-sectional social network analysis. ^e [79] applied longitudinal social network analysis. ^f RCTs = Random control trials; [82] applied clustered RCTs.