Outcome classification
The principle outcome variables were prevalence (n = 165) and incidence rates (n = 22), based on national cancer registry and hospitalization records. Although Korea has a national cancer registry, reporting was not complete during the time of follow-up, and consequently, hospital admission files were used to identify first admission events for CRC. An incident of CRC was coded as occurring, based on either a positive report from the national cancer registry or upon hospital admission for a cancer diagnosis [33]. According to the International Classification of Diseases, Tenth Revision (ICD-10), CRC was coded as C18-C20 [34].