Table 4. Methodological quality of cross-sectional studies included in the meta-analysis^*.

Item/Study	Khader, 2011			Ashford, 2010			Goel, 2004			Hanke, 1999			Eskenazi, 1995
	Yes	No	Unclear	Yes	No	Unclear	Yes	No	Unclear	Yes	No	Unclear	Yes	No	Unclear
1) Define the source of information (survey, record review)	√			√			√			√			√
2) List inclusion and exclusion criteria for exposed and unexposed subjects (cases and controls) or refer to previous publications	√			√				√		√			√
3) Indicate time period used for identifying patients	√				√			√		√			√
4) Indicate whether or not subjects were consecutive if not population-based	√			√			√			√			√
5) Indicate if evaluators of subjective components of study were masked to other aspects of the status of the participants	√			√			√			√			√
6) Describe any assessments undertaken for quality assurance purposes (e.g., test/retest of primary outcome measurements)		√			√			√			√			√
7) Explain any patient exclusions from analysis		√		√				√			√		√
8) Describe how confounding was assessed and/or controlled.	√			√			√			√				√
9) If applicable, explain how missing data were handled in the analysis	√				√			√		√			√
10) Summarize patient response rates and completeness of data collection	√				√			√		√			√
11) Clarify what follow-up, if any, was expected and the percentage of patients for which incomplete data or follow-up was obtained		√			√			√			√			√

* The definition/explanation of each column of the Agency for Healthcare Research and Quality is available from (http://www.ahrq.gov/research/findings).