Data source and study population

The NHIS database was used as the national registration database. The NHIS database contains all disease diagnoses and prescription information regarding the procedures and/or drugs in South Korea. The government supports financial expenses for treatment or medical examinations after registration of disease diagnoses and prescriptions. Moreover, the NHIS database contains demographic and socio-economic information of the South Korean population. The 10^th revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-10) codes is used to register any disease in the NHIS database.

This study included all adult patients (≥ 18 years old) who were diagnosed with lung cancer (C34 of ICD-10 code) and underwent lung cancer surgery between January 1, 2011, and December 31, 2018, in South Korea. In South Korea, the government covers almost all expenses (approximately 95%) involved in the treatment and examination of lung cancer after the registration of ICD-10 codes (C34); thus, all patients with lung cancer who underwent lung cancer surgery were included in the NHIS database.