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.

Persons who speak a language other than English at home were asked to report the language spoken, as well as their proficiency in English (see Language Usage and Ability to Speak English). This item was asked on a sample basis.

Respondents were instructed to report the language spoken most often, for persons speaking two or more non-English languages at home, or the first language learned, where the language spoken most often could not be determined.

The write-in entries of the language spoken were coded in census processing offices into 387 categories which arerecorded on basic records and public-use microdata files. Tables in PC30-1-C reports include the following categories:

English only, Chinese, French, German, Greek, Italian, Philippine languages, Polish, Spanish, other specified language, and unspecified language.

Data on languages spoken in the home are typically presented separately for persons 5 to 17 and 18 years old anti over. These data should not be interpreted as the number of people who are able to speak specified languages, since this question counts only persons who speak a language other than English at home.

The reported number of persons who speak a language other than English at home may be inflated slightly by a processing error. The total number of persons who speak a language other than English is inflated by approximately 0.4 percent nationwide. There is some geographic variation in the frequency of the errors, but no substantial spatial clustering has been discovered. Subsequent data products (STF 4, STF 5) will correct these errors, and thus may disagree with the estimates provided in STF 3.

Persons 5 years old and over are classified by whether they speak a language other than English at home, and, if so, by how well they speak English. Responses for persons under 5 are not tabulated. This item was asked on a sample basis.