Editing Census (section)

==Enumeration strategies==
[[File:Enumerator.jpg|thumb|An enumerator conducting a census survey using a mobile phone-based questionnaire in the rural [[Mutasa District]] in [[Zimbabwe]] in 2015]]
Historical censuses used direct field enumeration and assumed that the information collected was fully accurate, with no measurement error. Modern approaches take into account the problems of overcount and undercount and the coherence of census enumerations with other official sources of data.{{clarify|date=May 2019}} For instance, during the 2020 U.S. Census, the Census Bureau counted people primarily by collecting answers sent by mail, on the internet, over the phone, or using shared information through proxies. These methods accounted for 95.5 percent of all occupied housing units in the United States.<ref>{{cite web |last1=Percival |first1=Kelly |last2=Fong |first2=Clara |title=Understanding the Census Bureau's Methods for Completing the 2020 Count |url=https://www.brennancenter.org/our-work/research-reports/understanding-census-bureaus-methods-completing-2020-count |work=Brennan Center for Justice |access-date=2024-08-26 }}</ref> This reflects a realist approach to measurement, acknowledging that under any definition of residence there is a true value of the population{{Fix|text=gobbledegook}} but this can never be measured with complete accuracy. An important aspect of the census process is to evaluate the quality of the data.<ref>{{cite web |last1=Baffour |first1=Bernard |last2=Valente |first2=Paolo |date=13 May 2008 |title=Census Quality Evaluation: considerations from an international perspective |url=https://unece.org/fileadmin/DAM/stats/documents/ece/ces/ge.41/2008/sp.4.e.pdf |archive-url= |archive-date= |access-date=2025-02-05 |website=United Nations Economic Commission for Europe |publisher=United Nations Statistics Division}}</ref><ref>{{cite journal | last1 = Breiman | first1 = Leo | year = 1994 | title = The 1991 Census Adjustment: Undercount or Bad Data? | journal = [[Statistical Science]] | volume = 9 | issue = 4| pages = 458–75 | doi = 10.1214/ss/1177010259 | doi-access = free }}</ref>

Many countries use a post-enumeration survey to adjust the raw census counts.<ref>World Population and Housing Census Programme (2010) [http://unstats.un.org/unsd/demographic/standmeth/handbooks/Manual_PESen.pdf Post Enumeration Surveys: Operational guidelines] {{Webarchive|url=https://web.archive.org/web/20120503082524/http://unstats.un.org/unsd/demographic/standmeth/handbooks/Manual_PESen.pdf |date=2012-05-03 }}, United Nations Secretariat, Dept of Economic and Social Affairs, Statistics Division, Tech Report</ref> This works similarly to [[capture-recapture]] estimation for animal populations. Among census experts, this method is called dual system enumeration (DSE). A sample of households is visited by interviewers who record the details of the household as of census day. These data are then matched to census records, and the number of people missed can be estimated by considering the number of people who are included in one count but not the other. This allows adjustments to the count for non-response, varying between different [[demographic]] groups. An explanation using a fishing analogy can be found in "Trout, Catfish and Roach..."<ref>Benton, P. [http://www.ons.gov.uk/ons/guide-method/census/2011/the-2011-census/census-coverage-survey/trout--catfish-and-roach.pdf Trout, Catfish and Roach: The beginner's guide to census population estimates] {{Webarchive|url=https://web.archive.org/web/20120107223425/http://www.ons.gov.uk/ons/guide-method/census/2011/the-2011-census/census-coverage-survey/trout--catfish-and-roach.pdf |date=2012-01-07 }}, [[Office for National Statistics]], UK</ref> which won an award from the [[Royal Statistical Society]] for excellence in [[official statistics]] in 2011.

Triple system enumeration has been proposed as an improvement as it would allow evaluation of the statistical dependence of pairs of sources. However, as the matching process is the most difficult aspect of census estimation this has never been implemented for a national enumeration. It would also be difficult to identify three different sources that were sufficiently different to make the triple system effort worthwhile. The DSE approach has another weakness in that it assumes there is no person counted twice (over count). In ''de facto'' residence definitions this would not be a problem but in ''de jure'' definitions individuals risk being recorded on more than one form leading to double counting. A particular problem here is students who often have a term time and family address.

Several countries have used a system known as short form/long form.<ref>[http://www.ons.gov.uk/ons/guide-method/census/2011/what-is-a-census/other-methods-of-census-taking/index.html Other methods of census taking] {{Webarchive|url=https://web.archive.org/web/20120314160532/http://www.ons.gov.uk/ons/guide-method/census/2011/what-is-a-census/other-methods-of-census-taking/index.html |date=2012-03-14 }}, [[Office for National Statistics]], UK</ref> This is a [[Sampling (statistics)|sampling]] strategy that randomly chooses a proportion of people to send a more detailed questionnaire to (the long form). Everyone receives the short-form questions. This means more data are collected, but without imposing a burden on the whole population. This also reduces the burden on the statistical office. Indeed, in the UK until 2001 all residents were required to fill in the whole form but only a 10% sample was coded and analysed in detail.<ref>{{cite web |url=http://www.ons.gov.uk/ons/guide-method/census/census-2001/about-census-2001/introduction/index.html |title=Introduction to Census 2001 |publisher=Ons.gov.uk |date=2001-04-29 |access-date=2012-12-12 |archive-date=2013-01-17 |archive-url=https://web.archive.org/web/20130117043415/http://www.ons.gov.uk/ons/guide-method/census/census-2001/about-census-2001/introduction/index.html |url-status=live }}</ref> New technology means that all data are now scanned and processed. During the [[2011 Canadian census]] there was controversy about the cessation of the mandatory long-form census; the head of [[Statistics Canada]], [[Munir Sheikh]], resigned upon the federal government's decision to do so.<ref>{{cite web |author=The Canadian Press |url=http://www.680news.com/radio/680news/article/80353--text-of-munir-sheikh-s-resignation-statement |title=Text of Munir Sheikh's resignation statement |publisher=680News |date=2010-07-21 |access-date=2012-02-19 |url-status=dead |archive-url=https://web.archive.org/web/20111219103126/http://www.680news.com/radio/680news/article/80353--text-of-munir-sheikh-s-resignation-statement |archive-date=2011-12-19 }}</ref>

The use of alternative enumeration strategies is increasing<ref>{{cite web |url=http://www.ined.fr/en/publications/pop_soc/bdd/publication/1506/ |title=[INED&#93; Population and Societies |publisher=Ined.fr |access-date=2012-02-19 |archive-date=2013-01-17 |archive-url=https://web.archive.org/web/20130117052803/http://www.ined.fr/en/publications/pop_soc/bdd/publication/1506/ |url-status=live }}</ref> but these are not as simple as many people assume and are only used in developed countries.<ref>{{cite journal |last1=Kukutai |first1=Tahu |author-link=Tahu Kukutai |year=2014 |title=Whither the census? Continuity and change in census methodologies worldwide, 1985–2014 |journal=Journal of Population Research |volume=32 |pages=3–22 |doi=10.1007/s12546-014-9139-z |s2cid=154735445}}</ref> The Netherlands has been most advanced in adopting a census using [[administrative data]]. This allows a simulated census to be conducted by linking several different administrative databases at an agreed time. Data can be matched, and an overall enumeration established allowing for discrepancies between different data sources. A validation survey is still conducted in a similar way to the post-enumeration survey employed in a traditional census.

Other countries that have a population register use this as a basis for all the census statistics needed by users. This is most common among Nordic countries but requires many distinct registers to be combined, including population, housing, employment, and education. These registers are then combined and brought up to the standard of a statistical register by comparing the data from different sources and ensuring the quality is sufficient for official statistics to be produced.<ref>{{cite web|url=http://www.unece.org/fileadmin/DAM/stats/publications/Register_based_statistics_in_Nordic_countries.pdf |archive-url=https://web.archive.org/web/20121015113925/http://www.unece.org/fileadmin/DAM/stats/publications/Register_based_statistics_in_Nordic_countries.pdf |archive-date=2012-10-15 |url-status=live |title=Register-based statistics in the Nordic countries |website=Unece.org |year=2007 |access-date=2012-12-12}}</ref>

A recent innovation is the French instigation of a rolling census program with different regions enumerated each year so that the whole country is completely enumerated every 5 to 10 years.<ref>{{Cite web|url=http://www.statistics.gov.hk/wsc/STS017-P5-S.pdf |archive-url=https://web.archive.org/web/20170224211626/http://www.statistics.gov.hk/wsc/STS017-P5-S.pdf |archive-date=2017-02-24 |url-status=live|title=The French Rolling Census: a decade of experience|last=Durr|first=Jean-Michel and François Clanché}}</ref> In Europe, in connection with the 2010 census round, many countries adopted alternative census methodol\\ogies, often based on the combination of data from registers, surveys and other sources.<ref>{{cite web |url=http://www1.unece.org/stat/platform/display/censuses/2010+Population+Census+Round |title=2010 Population Census Round – Confluence |publisher=unece.org |access-date=2012-12-12 |archive-date=2012-11-07 |archive-url=https://web.archive.org/web/20121107120442/http://www1.unece.org/stat/platform/display/censuses/2010+Population+Census+Round |url-status=dead }}</ref>