2.1 | Data source
We conducted a nationwide population-based cohort study using claims and health checkup data from the National Health Insurance Service-National Sample Cohort (NHIS-NSC). The NHIS is a single-payer health care system for all Korean residents managed by the Korean government, covering more than 98% of the Korean population. The claims data encompasses sociodemographic variables; diagnosis statements defined by the International Classification of Diseases, 10th revision (ICD-10); prescriptions; and hospital visits dates. Our study protocol was approved by the NHIS review committee and Institutional Review Board of Kangbuk Samsung hospital (IRB No. KBSMC-07-034). Informed consent was waived by IRB as the data set provided from NHIS is deidentified to protect privacy.