2.1 | Study design and participants
This study was designed as a secondary data analysis using and interpreting data drawn from the third through thirteenth Korean Youth Risk Behavior Web-based Surveys (KYRBSs) completed across 7 years from 2013 to 2019. KYRBS was initiated by the Korean Ministry of Education, Ministry of Health and Welfare, and Centers for Disease Control and Prevention (KCDC) in 2005. The KYRBS is a cross-sectional, self-administered, anonymous, online survey that is conducted annually in a nationally representative sample of Korean adolescents aged 12–18 years. The Institutional Review Board (IRB) of the KCDC approved this online statistical research during the entire survey every year. In order to obtain a nationally representative sample, the KYRBS used the stratified three stage random cluster sampling method, which included stratification, sample allocation, and stratified cluster sampling, as is described. The study population was stratified by geographic region and school type to minimize sampling error. In sample allocation, 400 middle schools and 400 high schools were selected by proportional sampling to match the study population every year. In stratified cluster sampling, sample classes were selected by simple randomization sampling from the selected schools. All of the participants provided written informed consent (both directly and from their parents or legal guardians) for approval of survey access. Every student participated voluntarily and completed the survey by logging on to the survey’s Internet webpage at their school’s computer laboratory using a randomly assigned unique identification number. The participants were not able to skip to subsequent questions without providing proper answers to every question. The online system does not accept omitted responses. Data were considered to be missing if there was any logical error or if there was outlier. In the present study, we obtained the raw data that are publicly available from the online site of KYRBSs (https://www.cdc.go.kr/yhs/home.jsp). The reasons for drop-out or non-participation were not available. Our study protocol for secondary analysis and interpretation was reviewed and approved by the IRB of Samsung Changwon Hospital (IRB No. 2020-06-009).