In 1960, ascertained for persons 5 to 34 years of age, who were classified as enrolled in school if they attended regular school or college at any time since February 1, 1960. (Attendance at a nursery school, business or trade school, or adult education classes was not to be counted; regular schooling included kindergarten and schooling leading to an elementary school certificate, high school diploma, or college degree.) Persons enrolled in a regular school who did not actually attend because of illness, etc. were classified as enrolled in school. In 1970, ascertained for persons 3 years and older, who are classified as enrolled in school if they attended regular school or college at any time since February 1, 1970. (Regular schooling includes nursery school, kindergarten, and schooling leading to an elementary school certificate, high school diploma, or college degree.)