Table 2.

Analysis of basic characteristics of included studies.

Characteristic dimension	Category	Number of studies	Percentage	Number of participants	Average sample size
Study design	Randomised controlled trials	28	62.2%	2,456	87.7
	Quasi-experimental design	17	37.8%	1,436	84.5
Geographical distribution	Asia	23	51.1%	1,987	86.4
	Europe	13	28.9%	1,134	87.2
	North America	7	15.6%	623	89.0
	Other	2	4.4%	148	74.0
Age group	6–8 years	18	40.0%	1,456	80.9
	9–12 years	27	60.0%	2,436	90.2
Duration of intervention	2–4 weeks	12	26.7%	967	80.6
	4–8 weeks	21	46.7%	1,823	86.8
	>8 weeks	12	26.7%	1,102	91.8