When looking for and at data from the Census of Population and Housing, it's important to consider whether the questions were asked of all respondents or just a sample.
100% (Short Form) and Sample (Long Form) Questions
The 1940 census provided the prototype for the census today. It was the first census to develop and apply sampling techniques, thus creating the short form or 100% questionnaire and the long form, or the sample. Since then, the Census Bureau has continued to refine its sampling techniques but the terms 100% or sample are still the same.
The questions asked on both forms have changed over time; they reflect the changes in our society and the need for statistical data mandated by Federal legislative programs. See the Major Differences in Subject-Matter Content between 1990 and 2000 Census Questionnaires and the Census 2000 Questionnaires for the changes in that ten-year period, and for a longer historical perspective, Measuring America: The Decennial Censuses from 1790 to 2000, which includes the questionnaires and instructions to census takers.
It is expected that the American Community Survey (see the Intercensal Years tab) will replace the long form in the future.