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Census Undercount – Frequently Asked Questions (FAQ)

 What is the census undercount?

The census undercount (also known as census undercoverage) refers to the number of Canadian residents not recorded in the Statistics Canada census. In each census, despite census officials working hard to count the entire population on Census Day, some Canadian residents are missed and some are counted more than once. Statistics Canada adjusts official population estimates to include net undercoverage estimates (persons missed minus persons counted more than once).

How do you calculate total population including census undercount?

To learn how to calculate total population with undercount, please read the Guide to Calculating Total Population with Census Undercount (PDF 34KB, 1 page).

How are people missed or counted more than once in the Census?

People are missed in the census for many reasons, some of which include:

  • Census enumerators finding it difficult to locate or access certain households (eg. secondary suites)
  • People having difficulties understanding the questionnaire
  • Uncertainty about whether to include someone in a household
  • People with no usual residence
  • People being absent from their place of residence (e.g. travelling) during the census survey period
  • People refusing to participate in the Census (despite it being against the law)

Overcoverage occurs when Canadian residents are counted more than once (such as students living away from home being recorded by both themselves and their parents) and when non-Canadian residents (such as foreign residents, fictitious persons or pets) are mistakenly included in the census.

How does Statistics Canada find out who was missed or counted twice?

Following each census, the Reverse Record Check (RRC) estimates the number of persons missed in the census. This estimate is combined with the estimate of the number of persons counted more than once from the Census Overcoverage Study to calculate net undercoverage. The RRC study selects a sample of approximately 60,000 Canadian residents, who should have been counted in the 2001 Census. The sample represents the same target population as the census, but is obtained in a way that is independent from the census. For each person selected in the sample, it must be determined if the person was counted in the 2001 Census, if so how many times and if not why not (e.g. the person died, left the country, was missed by the census etc.). The RRC is a comprehensive record linkage and matching procedure, which systematically traces all persons in its sample, interviews them to obtain a census day address, and matches these persons to individual census documents. Results of these studies in combination with the census counts are used to produce current population estimates which take into account net undercoverage. Census coverage study results are usually available two years after Census Day and are used to revise and update population forecasts based on the 2006 Census results.


Statistics Canada. (2008). “Final Estimates of 2006 Census Coverage.” http://www.statcan.gc.ca/daily-quotidien/080929/dq080929d-eng.htm

Statistics Canada. (2008). “Census of Population - Reverse Record Check (RRC).” http://www.statcan.gc.ca/cgi-bin/imdb/p2SV.pl?Function=getSurvey&SDDS=3902&lang=en&db=imdb&adm=8&dis=2

 Other Resources

Table: Population Forecasts 2001-2031

Peel’s most recent population forecasts.

Please send comments and questions to:

Peel Data Centre
Region of Peel
Digital and Information Services,
Information Management Division
10 Peel Centre Dr., Suite A, 6th Flr.
Brampton, ON L6T 4B9