Item No	Recommendation	Page No.
Title and abstract	1	(a) Indicate the study's design with a commonly used term in the title or the abstract	1
		(b) Provide in the abstract an informative and balanced summary of what was done and what was found	1
Introduction
Background/rationale	2	Explain the scientific background and rationale for the investigation being reported	1 ~ 3
Objectives	3	State‐specific objectives, including any prespecified hypotheses	3
Methods
Study design	4	Present key elements of study design early in the paper	3 ~ 4
Setting	5	Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, follow‐up and data collection	3 ~ 4
Participants	6	(a) Give the eligibility criteria, and the sources and methods of selection of participants	3
Variables	7	Clearly define all outcomes, exposures, predictors, potential confounders and effect modifiers. Give diagnostic criteria, if applicable	3 ~ 4
Data sources/ measurement	8 a	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	3 ~ 4
Bias	9	Describe any efforts to address potential sources of bias	NA
Study size	10	Explain how the study size was arrived at	2
Quantitative variables	11	Explain how quantitative variables were handled in the analyses. If applicable, describe which groupings were chosen and why	3
Statistical methods	12	(a) Describe all statistical methods, including those used to control for confounding	4 ~ 5
		(b) Describe any methods used to examine subgroups and interactions	4 ~ 5
		(c) Explain how missing data were addressed	4
		(d) If applicable, describe analytical methods taking account of sampling strategy	4
		(e) Describe any sensitivity analyses	NA
Results
Participants	13 a	(a) Report numbers of individuals at each stage of study—For example, numbers potentially eligible, examined for eligibility, confirmed eligible, included in the study, completing follow‐up and analysed	5
		(b) Give reasons for non‐participation at each stage	NA
		(c) Consider use of a flow diagram	NA
Descriptive data	14 a	(a) Give characteristics of study participants (e.g. demographic, clinical, social) and information on exposures and potential confounders	5 ~ 6
		(b) Indicate number of participants with missing data for each variable of interest	NA
Outcome data	15 a	Report numbers of outcome events or summary measures	5 ~ 6
Main results	16	(a) Give unadjusted estimates and, if applicable, confounder‐adjusted estimates and their precision (e.g. 95% confidence interval). Make clear which confounders were adjusted for and why they were included	5 ~ 6
		(b) Report category boundaries when continuous variables were categorized	NA
		(c) If relevant, consider translating estimates of relative risk into absolute risk for a meaningful time period	NA
Other analyses	17	Report other analyses done—for example analyses of subgroups and interactions, and sensitivity analyses	NA
Discussion
Key results	18	Summarize key results with reference to study objectives	6 ~ 8
Limitations	19	Discuss limitations of the study, taking into account sources of potential bias or imprecision. Discuss both direction and magnitude of any potential bias	8
Interpretation	20	Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from similar studies, and other relevant evidence	8
Generalizability	21	Discuss the generalizability (external validity) of the study results	8
Other information
Funding	22	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	The Department of Education of Hebei Province and the Bureau of Science and Technology of Hebei Province

^a Give information separately for exposed and unexposed groups.