2.1. Data source
Data were collected from the National Health Insurance Service (NHIS)-Senior database, which included data for 558,147 individuals, approximately 10% of the elderly population in South Korea aged ≥60 years in 2002 (about 5.1 million).12 This study was approved by the institutional review board of Yonsei University Health System (4-2020-0798) and the need for informed consent was waived.