Table 2.

Results of quality assessment for cross-sectional studies.

First author, year	Selection				Comparability	Outcome
	Representativeness of the sample	Sample size	Nonrespondents	Ascertainment of the exposure	Based on the study design or analysis	Assessment of the outcome	Statistical test
Guan, 2009	+			+	+	++	+
Li, 2011	+			+	+	++	+
Zheng, 2011	+			+	+	++	+
Keinan-Boker, 2015	+		+	+	+	+	+
Wang, 2015	+		+	+	+	++	+
Han, 2019	+			+	+	++	+
Wang, 2019	+			+	+	++	+
Ning, 2019	+			+	+	++	+