Table 1. Methodological quality of cross-sectional studies according to the AHRQ standard.

	Luo et al. 199217	Yang et al. 199518	Sun et al. 199719	Feng et al. 200420	Liu et al. 200421	Bao et al. 200522	Sun et al. 201223
(1) Define the source of information (survey, record review)	Y	Y	Y	Y	Y	Y	Y
(2) List inclusion and exclusion criteria for exposed and unexposed subjects (cases and controls) or refer to previous publications	Y	Y	Y	Y	Y	Y	Y
(3) Indicate time period used for identifying patients	Y	Y	Y	U	Y	Y	Y
(4) Indicate whether or not subjects were consecutive if not population-based	Y	Y	Y	Y	Y	Y	Y
(5) Indicate if evaluators of subjective components of study were masked to other aspects of the status of the participants	U	U	U	U	U	U	U
(6) Describe any assessments undertaken for quality assurance purposes (e.g., test/retest of primary outcome measurements)	U	Y	Y	Y	U	U	U
(7) Explain any patient exclusions from analysis	U	U	U	U	U	U	U
(8) Describe how confounding was assessed and/or controlled	U	U	U	U	U	U	Y
(9) If applicable, explain how missing data were handled in the analysis	U	U	U	U	U	U	U
(10) Summarize patient response rates and completeness of data collection	Y	Y	Y	Y	Y	Y	Y
(11) Clarify what follow-up, if any, was expected and the percentage of patients for which incomplete data or follow-up was obtained	U	U	U	U	U	U	U