Education level was classified into three groups (elementary
school or lower, middle or high school, college or
higher). The household monthly income variable was
categorized into three groups (≤ 1000000 South Korean
won [KRW], 1500000 KRW < income ≤ 3000000 KRW, >
3000000 KRW). The duration of diabetes was defined as
the number of years since the patient received the diagnosis
of diabetes by a doctor, and the variable was divided
into three groups (