Age at last birthday, i.e., number of completed years from birth to April 1, 1980, based on replies to a question on month and year of birth. This item was asked on a complete-count basis.
Because of the central importance of the data on age, the question contains redundancies. The age entry on the basic tape record is derived from the FOSDIC entries of quarter and year of birth. For those persons who do not provide this information but who do provide "age at last birthday," the census enumerator or clerk uses an equivalency table to mark the appropriate FOSDIC circles. The item "age at last birthday" is used only secondarily because of the tendency of some people, in reporting their ages, to round off to "0" or "5" (and to report even rather than odd numbers). The write-in entries of month and year of birth are requested because some people have difficulty with (and therefore skip) the FOSDIC marking system in this question.
Age is tabulated by single years of age and by many different groupings such as 5-year age groups. Basic records identify single years (and quarter years on sample basic records) to 112. Public-use microdata samples show single years and quarters to 99, and 100 years or more.
Calculated as the value which divides the age distribution into two equal parts, one-half the cases falling below this value, one-half above. Median age is computed from the age intervals or groupings shown in the particular tabulation, and thus a median based on a less detailed distribution may differ slightly from a corresponding median for the same population based on a more detailed distribution. If the median falls in the terminal category, e.g., 75 years and over, the median is shown as the initial age of the category with a plus sign, e.g., 75+.
In previous censuses, undercoverage of the population has been associated with age. Young adults, especially Black males, were missed at a higher rate than other segments of the population. The same is true of centenarians.
Age data have been collected in each census since 1790. Counts in 1970 and 1980 for persons 100 years old
and over were substantially overstated.
See also: "Age of Householder".