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Census Technical Report: Coverage
The 2011 Census required the participation of the entire population of Canada, some 34.2 million people distributed over a territory of nine million square kilometres. Although data collection and processing have to meet high quality standards, it is impossible to eliminate all errors. To assess the usefulness of census data, users need to be aware of the conceptual framework and definitions used in conducting the census as well as the data collection and processing procedures, and the main sources of error, including, where possible, the size of the errors and any unusual circumstances that might limit the usefulness or interpretation of census data. With this information, users can assess the risks associated with using census data to draw conclusions or make decisions.
This technical report deals with coverage errors in the 2011 Census. There are two types of coverage errors: population undercoverage and population overcoverage. Population undercoverage refers to the error of excluding people who should have been enumerated. Population overcoverage refers to the error of either enumerating people more than once or including people who should not have been enumerated. Previous studies have shown that the error due to people who should not have been enumerated is negligible; consequently, that error is ignored here. Undercoverage is generally more common than overcoverage. In this context, the net impact of undercoverage and overcoverage on the size of a population of interest is population net undercoverage. Net undercoverage is the number of persons excluded who should have been enumerated (undercoverage) less the number of excess enumerations of persons enumerated more than once (overcoverage). Coverage error is one of the most important types of error since it affects not only the accuracy of the counts for the various census universes, but also the accuracy of all the census data that describe the characteristics of these universes.
Users of census data should be aware that the presence of coverage errors in the 2011 Census means that census products are subject to incomplete enumeration or duplicate enumeration. For example, undercoverage is higher among young adult males. For estimates of 2011 Census coverage errors for a variety of demographic and geographic levels and groupings, see Section 1.
Section 2 covers the conceptual framework of the 2011 Census and provides definitions of the population universe, the dwelling universe and usual place of residence. This is precisely what the census is intended to measure. Section 3 describes coverage error, sources of coverage error, census practices that minimize coverage error, and the conceptual framework for measuring coverage error. It is also an introduction to census coverage studies. The methodology used in the 2011 Census, in particular census frames, data collection, editing, coding and imputation, is covered in Section 4 and Section 5.
Census coverage error is measured by three studies. The 2011 Dwelling Classification Survey (DCS) addressed coverage error resulting from dwelling classification error. Census data were adjusted for this type of coverage error. The 2011 Reverse Record Check (RRC) measured population undercoverage. The 2011 Census Overcoverage Study (COS) measured population overcoverage. Census data are not adjusted for the coverage error identified by the RRC and the COS. Rather, Statistics Canada uses estimates of net undercoverage to produce demographic estimates.
The 2011 studies are quite similar to the 2006 studies, although some changes and improvements were made, particularly in the COS (for more information on this subject, see Section 8), including the following:
- Provincial and territorial record matching parameters were used for the COS instead of the national parameters used in 2006.
- Both steps of the COS now involve random sampling with manual verification, whereas in the 2006 COS, cases identified in the first step were all considered to be overcoverage.
The methodology and results of the 2011 Dwelling Classification Survey (DCS) are described in Section 6. This survey, conducted after census non-response follow-up, provides information used in the census to account for persons living in non-response dwellings and in occupied dwellings misclassified as unoccupied. This is done by imputing persons into the census database using the whole household imputation (WHI) procedure. The number of persons added through WHI is a key input for the estimates of population coverage error.
Estimates of coverage error rates are produced only for the population universe. The methodology and results of the 2011 RRC are described in Section 7. The methodology and results of the 2011 COS are described in Section 8. Section 9 shows how the results of the RRC and the COS are combined with census data to produce estimates of population coverage error and the associated standard errors. In view of the extensive use made of estimates of net undercoverage, it is important to undertake critical and detailed evaluations. Section 10 presents the results of evaluations performed for the RRC and the COS as well as an evaluation of the error of closure. The error of closure is the difference between demographic estimates whose base population is the 2006 Census adjusted for net undercoverage and 2011 Census data, also adjusted for net undercoverage.
Statistics Canada has conducted census population coverage studies since the first Reverse Record Check, which dates back to the 1961 Census.Footnote1 Section 11 provides a chronological review of coverage error from the 1971 Census to the 2011 Census.
Section 12 covers additional topics, including the concept of persons not enumerated and census participation by Indian reserves and Indian settlements.
This report was prepared by Karen Bruce, Colleen Clark, Abel Dasylva, Heather Farr, Michel Parenteau, Martin St-Pierre, Christian Thibault and Robert-Charles Titus of the Social Survey Methods Division, and Denis Morissette of the Demography Division.
Normand Laniel and David Dolson, of the Social Survey Methods Division, contributed valuable comments on earlier drafts, which improved the content and readability of the final report. We gratefully acknowledge the support of members of the Census Operations Division, the Demography Division and the Social Survey Methods Division.
For additional information on census concepts, variables and geography, please see the 2011 Census Dictionary. For additional information about the census process, please see the 2011 Census reference materials.
- Section 1 Estimates of population coverage error
- Section 2 Census universes
- Section 3 Population coverage error
- Section 4 Census data collection
- Section 5 Census data processing
- Section 6 Dwelling Classification Survey
- Section 7 Reverse Record Check
- Section 8 Census Overcoverage Study (COS)
- Section 9 Estimation
- Section 10 Evaluation of coverage studies
- Section 11 Historical estimates of population coverage error
- Section 12 Special topics
- Appendix A Reverse Record Check Survey questionnaires
- Appendix B Abbreviations
- Footnote 1
The first RRC was conducted in 1961, but there was no frame of persons missed in the previous census. The 1966 RRC used the results of the 1961 RRC to construct the frame of persons missed in the 1961 Census.