Table 3. Risk of bias in the included studies.

Study	Item 1	Item 2	Item 3	Item 4	Item 5	Item 6	Item 7	Item 8	Item 9	Item 10
Chen 2020 (9)	Yes	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Zhong 2020 (10)	Yes	No	No	Yes	UN	Yes	UN	Yes	Yes	Yes
Zheng 2020 (11)	No	No	Yes	Yes	No	Yes	No	Yes	Yes	UN
Qi 2020 (12)	Yes	No	Yes	Yes	No	No	No	Yes	Yes	UN
Zhu 2020 (13)	No	No	Yes	Yes	No	Yes	No	Yes	Yes	UN
Yang 2020 (14)	No	No	Yes	Yes	No	Yes	No	Yes	Yes	UN
Song 2003 (15)	Yes	Yes	Yes	Yes	Yes	No	Yes	Yes	No	No
Zhang 2004 (16)	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	No	No
Chan 2007 (17)	Yes	No	Yes	Yes	UN	Yes	Yes	Yes	Yes	—
Du 2009 (18)	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	—	—
Gautret 2013 (19)	Yes	UN	Yes	Yes	Yes	—	Yes	Yes	—	Yes
Bener 2004 (20)	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Sahin 2015 (21)	Yes	UN	Yes	Yes	Yes	—	Yes	Yes	—	Yes
Jardine 2015 (22)	Yes	Yes	Yes	Yes	—	—	Yes	Yes	UN	—
Alqahtani 2016 (23)	Yes	UN	Yes	Yes	UN	—	Yes	Yes	Yes	—
Huang 2016 (24)	Yes	No	Yes	Yes	No	No	Yes	Yes	Yes	—
Alhomoud 2017 (25)	Yes	No	No	Yes	—	—	Yes	Yes	UN	—
Bawazir 2018 (26)	Yes	No	Yes	Yes	—	Yes	Yes	Yes	Yes	—
Migault 2019 (27)	Yes	No	No	Yes	UN	—	Yes	—	—	—
Zhu 2004 (28)	Yes	No	Yes	Yes	No	No	Yes	Yes	Yes	—
Zhong 2004 (29)	Yes	No	Yes	Yes	No	Yes	Yes	Yes	No	No
Alqahtani 2017 (30)	Yes	Yes	Yes	UN	UN	Yes	UN	Yes	Yes	Yes
Almutairi 2015 (31)	UN	Yes	Yes	Yes	UN	Yes	UN	Yes	Yes	Yes
Al-Mohrej 2016 (32)	Yes	Yes	Yes	Yes	UN	Yes	UN	Yes	Yes	Yes

1, Sample representativeness; 2, sampling method; 3, sample size; 4, study subjects and setting; 5, coverage of the identified sample; 6, using of standardized criteria for the measurement; 7. reliability of the measurement; 8, appropriateness of the statistical analysis; 9, confounding factors/subgroups/differences; 10, objectiveness of the criteria of subpopulations. UN, unknown; —, not applicable.