1. U.S. Census Bureau. 1940 Decennial Census population and housing questionnaires [Internet]. Available from: https:// www.census.gov/history/pdf/1940_population_questionnaire. pdf and https://www.census.gov/history/pdf/1940_housing_ questionnaire.pdf.
2. Groves R.M., Three eras of survey research, Public Opinion Quarterly 75(5) (2011).
3. U.S. Census Bureau. History of the 1990 Census [Internet]. See p. 6-48 through 6-55. Available from: http://www.census . gov/history/pdf/1990proceduralhistory.pdf See also the histories of the 1970, 1980, and 2000 Censuses; available from: http://www.census.gov/history/www/through_the_decades/ overview/.
4. U.S. Census Bureau. History: 2000 Census of population and housing [Internet]. Page 519. Available from: http://www. census.gov/history/pdf/Census2000v2.pdf.
5. U.S. Census Bureau. History: 2000 Census of population and housing [Internet]. p. 35. Available from: http://www.census. gov/history/pdf/Census2000v1.pdf.