Data on educational attainment were derived from answers to the questionnaire which was asked of sample persons.  Data are tabulated as attainment for persons 15 years old and over.  Persons are classified according to the highest level of school completed or the highest degree received.  The question includes instructions to report the level of the previous grade attended or the highest degree received for persons currently enrolled in school.  The question included response categories which allowed persons to report completing the 12th grade without receiving a high school diploma, and which instructed respondents to report as "high school graduate(s)" - persons who received either a high school diploma or the equivalent, for example, passed the Test of General Educational Development (G.E.D.), and did not attend college.  (On the Military Census Report questionnaire, the lowest response category was "Less than 9th grade.").

Instructions included in the respondent instruction guide, which was mailed with the census questionnaire, further specified that schooling completed in foreign or upgraded school systems should be reported as the equivalent level of schooling in the regular American system; that vocational certificates or diplomas from vocational, trade, or business schools or colleges were not to be reported unless they were college level degrees; and that honorary degrees were not to be reported.  The instructions gave "medicine, dentistry, chiropractic, optometry, osteopathic medicine, pharmacy, podiatry, veterinary medicine, law, and theology" as examples of professional school degrees, and specifically excluded "barber school, cosmetology, or other training for a specific trade" from the professional school category.  The order in which they were listed suggested that doctorate degrees were "higher than professional school degrees, which were "higher" than master's degrees.

High School Graduate or Higher - Includes persons whose highest degree was a high school diploma or its equivalent, persons who attended college or professional school, and persons who received a college, university, or professional degree.  Persons who reported completing the 12th grade but not receiving a diploma are no included.

Not Enrolled, Not High School Graduate - Includes persons of compulsory school attendance age or above who were not enrolled in school and were not high school graduates; these persons may be taken to be "high school dropouts."  There is no restriction on when they "dropped out" of school, and they may have never attended high school.