Chapter 6 – Data dissemination for NHS standard products

Data suppression

The data that Statistics Canada disseminates are subject to various automated and manual processes to determine whether they should be suppressed. These processes are carried out to maintain confidentiality and data quality.

Suppression for confidentiality reasons

Confidentiality refers to the assurance that Statistics Canada will not disclose any information that could be used to identify respondents. Various confidentiality rules are applied to all data that are released or published to prevent the publication or disclosure of any information deemed confidential. If necessary, data are suppressed to prevent direct or residual disclosure of identifiable data. Consequently, geographic areas whose population is below a certain threshold are not published. For details on the confidentiality suppression thresholds, please see the Data Quality and Confidentiality Standards and Guidelines for the NHS.

Suppression due to estimate quality

Following the review of data quality, the dissemination of data whose quality is not considered satisfactory can be restricted if necessary. Quality indicators are produced for all standard place of residency geographies for which data are released.

The global non-response rate is an important measure of the quality of NHS estimates. It combines household and item non-response. This measure is used for the 2011 Census, just as it was in 2006 for dissemination of the Census, including the long form. In the specific case of the NHS, the global non-response rate is weighted to take account of the initial sample and the subsample used in non-response follow-up. It is calculated and presented for each geographic area.

As noted in Section 3.1, there is non-response bias when a survey's non-respondents are different from its respondents. The higher the non-response is, the greater the risk of non-response bias. For the NHS, a number of measures were taken to mitigate the potential effects of non-response bias. Despite those efforts, the risk of non-response bias remains.

The global non-response rate is also used as a main dissemination criterion associated with the quality of the NHS estimates. For example, the NHS estimates for any geographic area with a global non-response rate greater than or equal to 50% are not published in the standard products. The estimates for such areas have such a high level of error that they should not be released under most circumstances.

The 50% threshold is based on studies of the global non-response rate in relation to the indicators of non-response bias (see Section 5.5). The studies showed that with a global non-response rate of 50% or more, the bias was so large that the estimates were not of sufficiently high quality.

At the Canada level, the NHS's global non-response rate is 26.1%. Item non-response made a much smaller contribution to the global non-response rate than household non-response. Table 2 shows the NHS's global non-response rate for Canada and for each province and territory.

Coverage of published NHS data

Canada has a total of 147 census metropolitan areas (CMAs) and census agglomerations (CAs). For all of these areas, the global non-response rate is less than 50%, and published NHS data are available in standard products. In addition, NHS standard products are available for all 293 census divisions (CDs) and all 308 federal electoral districts (FEDs).

With a global non-response rate threshold of 50% for the release of NHS data, estimates are published for a majority of census subdivisions (CSDs), or municipalities. Of the 4,567 CSDs with an estimated population of more than 40 (for confidentiality reasons, those with a population of less than 40 are not published), NHS estimates are available in standard products for 3,439 (75.3%). Table 3 shows the distribution of published CSDs by province and territory. The proportion ranges from 100% for the Northwest Territories to 57.4% for Saskatchewan. Table 3 also shows the proportion of each province's and territory's population covered by published CSDs. It ranges from 100% for the Northwest Territories to 79.4% for Prince Edward Island. Overall, data are available for 96.6% of the Canadian population targeted by the NHS.

The NHS is the largest voluntary survey ever conducted by Statistics Canada. During data collection, Statistics Canada used a wide variety of tools to encourage as many people as possible to complete the NHS. As a result, the final response rate was 68.6%, similar to the rates for Statistics Canada's other voluntary surveys.

In some small areas, the response rate was not high enough to produce a valid statistical picture. For those cases, users are encouraged to use data for a higher geography. For most areas, however, the responses received made it possible to produce good-quality estimates that will meet the needs of many users.