흡연 여부는 현재 피움과 가끔 피움을 흡연자로, 과거엔 피웠으나 현재 피우지 않음을 비흡연자로 구분하였다.
For smoking status, current and occasional cigarette smokers were classified as smokers, and those who smoked in the last although not presently smoked had been classified as nonsmokers.