Table 5. Example of Quality Assessment of Included Studies .

	Question	Wordsworth S, et al: 2001	Choi HCW et al, 2013
1	(a) Indicate the study’s design with a commonly used term in the title or the abstract	Yes	Yes
2	(b) Provide in the abstract an informative and balanced summary of what was done and what was found	Yes	Yes
3	Explain the scientific background and rationale for the investigation being reported	Yes	Yes
4	State specific objectives, including any prespecified hypotheses	Yes	Yes
5	Present key elements of study design early in the paper	Yes	Yes
6	Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, follow-up, and data collection	Yes	Yes
7	(a) Give the eligibility criteria, and the sources and methods of selection of participants	Yes	Yes
8	Clearly define all outcomes, exposures, predictors, potential confounders, and effect modifiers. Give diagnostic criteria, if applicable	Yes	Yes
9	For each variable of interest, give sources of data and details of methods of assessment (measurement). Describe comparability of assessment methods if there is more than one group	Yes	Yes
10	Describe any efforts to address potential sources of bias	No	No
11	Explain how the study size was arrived at	Yes	Yes
12	Explain how quantitative variables were handled in the analyses. If applicable, describe which groupings were chosen and why	Yes	Yes
13	(a) Describe all statistical methods, including those used to control for confounding	Yes	Yes
14	(b) Describe any methods used to examine subgroups and interactions	No	No
15	(c) Explain how missing data were addressed	No	Yes
16	(d) If applicable, describe analytical methods taking account of sampling strategy	Yes	Yes
17	(e) Describe any sensitivity analyses	No	No
18	(b) Give reasons for non-participation at each stage	No	No
19	(a) Give characteristics of study participants (eg demographic, clinical, social) and information on exposures and potential confounders	Yes	Yes
20	(b) Indicate number of participants with missing data for each variable of interest	No	No
21	Report numbers of outcome events or summary measures	Yes	Yes
22	(a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and their precision (eg, 95% confidence interval). Make clear which confounders were adjusted for and why they were included	Yes	Yes
23	(b) Report category boundaries when continuous variables were categorized	Yes	Yes
24	Summarise key results with reference to study objectives	Yes	Yes
25	Discuss limitations of the study, taking into account sources of potential bias or imprecision. Discuss both direction and magnitude of any potential bias	Yes	Yes
26	Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from similar studies, and other relevant evidence	Yes	Yes
27	Discuss the generalisability (external validity) of the study results	Yes	Yes
28	Give the source of funding and the role of the funders for the present study and, if applicable, for the original study on which the present article is based	No	Yes
29	Does a detailed description of goods or services in question offered to the respondents?	No	Yes
30	Does the information and attributes expressed in goods or services scenarios is obtained from user or key informant assessments (e.g. focus groups, Delphi panels, interviews etc)?	No	Yes
31	Was there a pilot study conducted to assess the survey tool/design?	No	No
32	Does the survey involve face to face interviews?	No	No
33	Were those involved in data collection adequately trained?	No	NA