Table 2.

Newcastle-Ottawa scale for assessing the quality of included studies

Study design	Author, year	Selection (Max = 4)	Comparability (Max = 2)	Outcome (Max = 3)	Overall quality score (Max = 9)
Cross-sectional study	Magee et al. 2018 [8]	3	2	3	8
Study design	Author, year	Selection (Max = 4)	Comparability (Max = 2)	Exposure (Max = 3)	Overall quality score (Max = 9)
Case-control study	Marupuru et al. 2017 [19]	4	1	2	7
Study design	Author, year	Selection (Max = 4)	Comparability (Max = 2)	Outcome (Max = 3)	Overall quality score (Max = 9)
Cohort study	Tseng 2018 [7]	4	2	2	8
	Pan et al. 2018 [13]	4	2	2	8
	Ma et al. 2018 [21]	4	1	3	8
	Lin et al. 2018 [10]	4	2	2	8
	Lee et al. 2018 [9]	4	2	2	8
	Degner et al. 2018 [12]	4	2	2	8
	Lin et al. 2017 [20]	4	2	2	8
	Lee et al. 2017 [11]	4	2	2	8
	Singhal et al. 2014 [4]	3	2	1	6