학력은 고등학교 졸업, 전문대학 졸업, 4년제 대학 졸업, 대학원 석사 졸업, 대학원 박사 졸업을 각각 더미변수로 하였다.
As for the academic background, high school graduation, junior college graduation, four-year college graduation, graduate school master's graduation, and graduate doctoral graduation were each dummy variable.