Table 3: Agency for Healthcare Research and Quality (AHRQ) checklist to assess the quality of the included observational studies.

ARHQ Methodology Checklist for Cross-sectional study
(http://www.ncbi.nlm.nih.gov/books/NBK35156/)		 Stavroulopoulos et al. Huang et al. Ersoy et al. Orlic et al. Baszko-Blaszyk et al. Fidan et al. Sit et al. Aggarwal et al.
1. Define 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 - + U U - + U -
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) + + U + - + + +
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 NA NA U NA - + NA NA
10. Summarize patient response rates and completeness of data collection + + - - U + - +
11. Clarify what follow-up, if any, was expected and the percentage of patients for which incomplete data or follow-up was obtained NA + NA U - NA NA NA

+ = Yes; - = No; U = Unclear; NA = Not applicable.