2011 Census: Data Quality and Confidentiality Standards and Guidelines (Public)
Data quality practices

The following section describes the methods used to restrict the dissemination of census data of unacceptable quality.

Data quality measures

Data quality indicators

Data quality indicators (commonly referred to as data quality flags) are attached to each standard geographic area disseminated. In the census database environment, the data quality indicators consist of a five-digit numeric field. In electronic products browsed via Beyond 20/20, these flags are displayed as a five-digit numeric code (example: 0 2 1 0 0). On the census website, flagging to end users of partially enumerated areas is done through the use of symbols.

Incompletely enumerated Indian reserves and Indian settlements

In the 2011 and previous censuses, enumeration was not completed on some Indian reserves and settlements, due to non-participation. Data quality rules require these incompletely enumerated Indian reserves and settlements be identified and removed from products. As well, higher-level geographic areas containing these areas must be identified in the products. These higher-level indicators are automatically included in output tabulations in Beyond 20/20, CSV and 'flat file' formats. For a list of 2011 incompletely enumerated Indian reserves and settlements, users can go to the reference materials section of the census website.

Although census data are not available for incompletely enumerated Indian reserves and settlements, the areas themselves are included as part of the standard geographic hierarchies on the census database.

Global response rates

Global response rates are determined for each of the census geographic areas. These areas are flagged on the database according to the non-response rate. Geographic areas with a non-response rate higher than or equal to 25% are suppressed from tabulations. Geographic areas with a global non-response rate higher than or equal to 5% and lower than 25% are broken into two categories and are flagged according to the following ranges: falling between 5% and 10% and falling between 10% and 25%. These geographic areas are identified in tabulations, but not suppressed. In electronic products, a numeric flag is provided with the area identifier indicating low data quality.

Population and dwelling counts error flag

After the release of the population and dwelling counts, errors are occasionally uncovered in the data. It is not possible to make changes to the census data presented. Users can, however, obtain the population and dwelling count amendments, listed by census subdivisions and other levels of geography, by visiting the 2011, 2006 or 2001 census portion of the Statistics Canada website at www.statcan.gc.ca.

Not applicable data quality indicator (20% sample data quality flag)

The fourth numeric code of the five-digit data quality indicator on the database is not applicable for the 2011 Census, and it is automatically set to zero for each geographic area. The value that resides on the database is a place holder for historical reasons; in 2006 and previous censuses, all five digits were applicable, the fourth digit was the 20% sample data quality flag.

2006 adjusted population flag

Users wishing to compare 2011 Census data with those of other censuses should take into account that the boundaries of geographic areas may change from one census to another. In order to facilitate comparison, the 2006 Census counts are adjusted as needed to take into account boundary changes between the 2006 and 2011 censuses. The flag is also used to refer to corrections to the 2006 counts and to identify areas that have been created since 2006, such as newly incorporated municipalities (census subdivisions) and new designated places. However, most of these flags are the result of boundary changes.

Table below describes the data quality indicator field and its contents. Note that a zero in any of the five digits is the default for the respective indicator and means that no data quality action is required.

Data quality indicators – 2011 Census
Digit Description Flag Flag description
1st (0XXXX) Incomplete enumeration flag 0 Default.
1 Incompletely enumerated Indian reserve or Indian settlement (suppressed).
2 Excludes census data for one or more incompletely enumerated Indian reserves or Indian settlements.
2nd (X0XXX) Data quality flag 0 Default.
1 Data quality index showing, for the short census questionnaire (100% data), a global non‑response rate higher than or equal to 5% but lower than 10%.
2 Data quality index showing, for the short census questionnaire (100% data), a global non‑response rate higher than or equal to 10% but lower than 25%.
3 Data quality index showing, for the short census questionnaire (100% data), a global non‑response rate higher than or equal to 25% (suppressed).
3rd (XX0XX) Population and dwelling counts error flag 0 Default.
1 An error exists in the 2011 population and dwelling counts for this area. For further details, please refer to the population and dwelling counts data section of the 'Notes' file.
2 In 2006, the population and/or dwelling counts for this census subdivision were found to be incorrect. Since it is not possible to make changes to the 2006 Census data presented in these tables, the 2006 data should be used with caution. For further details, please refer to the population and dwelling counts data section of the 'Notes' file.
3 Both the 2011 and 2006 population and/or dwelling counts for this area were found to be incorrect. Since it is not possible to make changes to the census data presented in these tables, these counts should be used with caution. For further details, please refer to the population and dwelling counts data section of the 'Notes' file.
4th (XXX0X) Not applicable 0 Default.
5th (XXXX0) 2006 adjusted population flag 0 Default.
1 2006 adjusted count; most of these are the result of boundary changes.

Note: The data quality flag does not apply to the population and dwelling counts.

Please refer to the 2006 Data Quality and Confidentiality Guidelines document (Public) for the flag legends for historical census years.

Other methods of data quality suppression

The methods of suppression mentioned to this point provide sufficient data quality suppression and identification for most census data products. However, in some products, the specifying area or production area may require that additional data quality suppression be performed. Examples of additional suppression could include increasing population thresholds or applying distribution or cell suppression. These are typically product-specific requirements and therefore are not part of the automated suppression systems. In all cases, some form of manual process is required.

Calculation of order statistics

For variables which have integer values, a median (or other quantile) is calculated using linear interpolations to give the variable a decimal, even if the variable is an integer. This is done to provide a sense of the relative position of the median record among those records that have the same value (the median). Therefore, a value of 23.46 means that the record in the middle (the median) has Age = 23 and 46% of all records with Age = 23 lie to the left of the middle. The following set {23, 23, 23, 23, 23, 23, 23, 23, 23} (the median is bolded) yields 23.11 as the calculated/reported median, for example.

Data quality rule for disseminating data for population aged 100 and older

Data for the population aged 100 years and older cannot be disseminated in single years of age. For custom requests that require a more detailed breakdown than provided in standard data products, in which the population aged 100 years and older is grouped together, the most detailed age breakdown which can be provided is as follows, and it can only be provided for 'Canada':

Total population 100 years and older
100 years to 104 years
105 years to 109 years
110 years and older

Data quality rule for disseminating data on same-sex and opposite-sex couples

The questionnaires of the 2011 Census of Population and the 2011 National Household Survey introduced for the first time a specific response on household relationships to determine the number of same-sex married couples. Analysis of the data on same-sex married couples has shown that there may be an overestimation of this family type and marital status. The 2011 Census shows a total of 64,575 same-sex couples in Canada, of which 21,015 are married couples. The range of overestimation of both these counts, at the national level, is between 0 and 4,500.

For levels of geography such as Canada, provinces, territories and census metropolitan areas (CMAs), counts are generally higher, so the potential overestimation is expected to be small in relative terms; however, the data should still be interpreted with caution.

At lower levels of geography, the same potential overestimation could be relatively large, and not only should the data be interpreted with caution, but certain suppression rules restrict their publication. These rules apply to both the 2011 Census and the 2011 National Household Survey.

First, the breakdown of same-sex couples or opposite-sex couples by conjugal status, that is, whether they are married or living common law, cannot be disseminated for geographic areas other than Canada, provinces, territories and CMAs.

Second, data cannot be disseminated that identify either same-sex or opposite-sex couples (in total, married or living common law) of any area with a population of less than 5,000 (as measured in the 2011 Census for private households).

In summary,

  • All data may be disseminated for same-sex or opposite-sex couples for Canada, provinces, territories, census metropolitan areas (CMAs), although they should still be interpreted with caution.
  • Data on same-sex couples and opposite-sex couples may be disseminated for other geographic areas if they have a population of 5,000 or more, provided that the breakdown by conjugal status (married, living common law) is not included.
  • No data may be disseminated that identify any same-sex or opposite-sex couples for areas of population less than 5,000.
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