Canadian COVID-19 Antibody and Health Survey (CCAHS)

Detailed information for Follow-up Questionnaire, 2023

This follow-up to the Canadian COVID-19 Antibody and Health Survey (CCAHS - Follow-up Questionnaire, 2023) collected new and updated information about health. The questions touched on changes in vaccination status, reinfection with the virus that causes COVID-19, symptoms of COVID-19 and impact on daily life, health conditions and the use of health care services.

Data release - December 8, 2023

• Questionnaire(s) and reporting guide(s)
• Description
• Data sources and methodology
• Data accuracy

Description

Understanding how the COVID-19 pandemic has affected the health and well-being of Canadians is an important step toward Canada's recovery. To support this goal, Statistics Canada and the Public Health Agency of Canada partnered to conduct a follow-up to the Canadian COVID-19 Antibody and Health Survey (CCAHS - Follow-up Questionnaire, 2023). The data from this survey will be combined with data from Cycle 2 of the Canadian COVID-19 Antibody and Health Survey, which was conducted between April and August 2022, to produce the evidence needed for informed decision-making.

This follow-up collected updated information about health. The questions touched on changes in vaccination status, reinfection with the virus that causes COVID-19, symptoms of COVID-19 and impact on daily life, health conditions and the use of health care services.

Reference period: Varies according to the question (e.g., Since the start of the pandemic, since your first COVID-19 infection, etc.).

Collection period: May to June 2023

Subjects

• Diseases and health conditions
• Health
• Lifestyle and social conditions

Data sources and methodology

Target population

The target population for the survey was adults 18 years of age and older living in the 10 provinces.

The observed population excluded: persons living in the three territories; persons living on reserves and other Indigenous settlements in the provinces; members of the Canadian Forces living on a base; the institutionalized population and residents of certain remote regions.

Instrument design

The survey collected data on changes in vaccination status, reinfection with the virus that causes COVID-19, symptoms of COVID-19 and impact on daily life, health conditions and the use of health care services.

The questionnaire followed standard practices and wording used in a computer-assisted interviewing environment, such as the automatic control of flows that depend upon answers to earlier questions and the use of edits to check for logical inconsistencies and capture errors. The computer application for data collection was tested extensively.

Sampling

This was a sample survey with a cross-sectional design and a longitudinal follow-up.

The Canadian COVID-19 Antibody and Health Survey - Follow-up Questionnaire, 2023 (CCAHS - Follow-up Questionnaire, 2023) included all participants from the Canadian COVID-19 Antibody and Health Survey (CCAHS) Cycle 2 who provided a valid email address while responding to the survey.

In total, a sample of 25,544 people was selected for the CCAHS - Follow-up Questionnaire, 2023, which represented 78.5% of the CCAHS Cycle 2 respondents.

Data sources

Data collection for this reference period: 2023-05-23 to 2023-06-19

Responding to this survey is voluntary.

Data are collected directly from survey respondents and derived from other Statistics Canada surveys.

1- Collection method: Electronic questionnaire

Respondents from the Canadian COVID-19 Antibody and Health Survey (CCAHS) Cycle 2 who provided a valid email were sent an invitation to participate in this follow-up survey.

2- Follow-up methods:
Respondents were sent up to 3 reminder emails.

3- Languages offered:
The questionnaire was available in English and French.

4- Average time to complete the survey:
The electronic questionnaire took on average 10 minutes to complete.

Data integration conducted including: To enhance the data from this survey and to reduce the response burden, Statistics Canada combined the information provided with information from the Canadian COVID-19 Antibody and Health Survey (CCAHS) - Cycle 2.

View the Questionnaire(s) and reporting guide(s).

Error detection

Electronic files containing the daily transmissions of completed respondent survey records were combined to create the "raw" survey file. Before further processing, verification was performed to identify and eliminate potential duplicate records and to drop non-response and out-of-scope records.

In addition, some out-of-scope respondent records were found during the data clean-up stage. All respondent records that were determined to be out-of-scope and those records that contained no data were removed from the data file.

After the verification stage, editing was performed to identify errors and modify affected data at the individual variable level. The first editing step was to identify errors and determine which items from the survey output needed to be kept on the survey master file. Subsequent to this, reclassification of other-specify responses was completed as required.

Imputation

Some variables for which imputation was carried out are available, however imputation of these variables was completed for the CCAHS Cycle 2 then linked to the follow-up data file.

Estimation

The estimation of population characteristics from a sample survey is based on the premise that each person in the sample represents a certain number of other persons in addition to themselves. This number is referred to as the survey weight. The process of computing survey weights for each survey respondent involves several steps.

1) Each selected person in the CCAHS - Follow-up Questionnaire sample is given an initial weight equal to their electronic questionnaire (EQ) weight from the CCAHS Cycle 2 (across all collection periods) prior to the calibration step.

2) Based on whether a CCAHS Cycle 2 respondent provided a valid email address, CCAHS Cycle 2 respondents can be divided into two groups, CCAHS-Follow-up Questionnaire sample and CCAHS-Follow-up Questionnaire non-sample. The weights of the CCAHS-Follow-up Questionnaire non-sample units are redistributed to the CCAHS-Follow-up Questionnaire sample units within response homogeneity groups (RHGs). To create the RHGs, a scoring method based on logistic regression model (built using some of the CCAHS Cycle 2 questionnaire responses) is used to determine the propensity of each unit to provide a valid email address and these response probabilities are used to divide the CCAHS Cycle 2 respondents into groups with similar response propensities.

3) During data collection, some units in the CCAHS - Follow-up Questionnaire sample resulted in nonresponse. Similar to step 2, the weights of the nonrespondents are redistributed to respondents within RHGs constructed using a logistic regression model.

4) Using the control totals for known COVID-19 vaccination cases, and persons reporting having been vaccinated against COVID-19, a post-stratification is applied to the nonresponse-adjusted weights.

5) The person weights are calibrated so that the sum of the weights match demographic population counts at the scale of the Canadian provinces by age groups and by sex. The weights are also calibrated to demographic counts for large Census Metropolitan Areas (CMAs) and groupings of small CMAs.

6) Note that following a series of adjustments applied to the weights, it is possible that some units will have weights that stand out from the other weights to the point of being aberrant. Some respondents may actually represent an abnormally high proportion in their group and therefore strongly influence both the estimates and the variance. To avoid this situation, a respondent weight that contributes aberrantly to the provincial total is adjusted downward using a method known as "winsorization." In this process, respondent weights that are considered to be outliers are replaced by the highest non-outlier weight for that province. All of the weights are then adjusted to redistribute the surplus weight (the part of the weight that is higher than the highest non-outlier weight). This is done by multiplying the non-outlier weights by an adjustment factor to create the winsorized weights.

7) A second calibration (an exact repetition of the first calibration) is applied to the winsorized weights to produce the final weight.

Sampling variance estimation is based on a resampling method called the bootstrap.

The Generalized Estimation System (G-Est) was used to generate the survey weights and bootstrap weights.

Quality evaluation

While quality assurance mechanisms are applied at all stages of the statistical process, the validation and detailed review of data by statisticians is the final verification of quality prior to release. Many validation measures were implemented, they include:

a. Verification of estimates through cross-tabulations

b. Consultation with stakeholders internal to Statistics Canada

c. Consultation with external stakeholders

Survey weights were also adjusted to minimize any potential bias that could arise from survey non-response; non-response adjustments and calibration using available auxiliary information were applied and are reflected in the survey weights provided with the data file.

Extensive validations of survey estimates were also performed and examined from a bias analysis perspective. Despite these rigorous adjustments and validations, the high non-response increases the risk of a remaining bias and the magnitude with which such a bias could impact estimates produced using the survey data. Therefore, users are advised to use the CCAHS data with caution, especially when creating estimates for small sub-populations or when comparing to other publicly available sources of data.

Disclosure control

Statistics Canada is prohibited by law from releasing any information it collects that could identify any person, business, or organization, unless consent has been given by the respondent or as permitted by the Statistics Act. 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.

Estimates with less than 5 positive counts in the numerator are suppressed for confidentiality reasons.

Estimates for which the effective sample size is below 30 are also suppressed.

Revisions and seasonal adjustment

This methodology does not apply.

Data accuracy

The survey aims at producing unbiased national and provincial estimates of good quality. Age group and sex breakdowns are also possible, but careful considerations of sample size and quality indicator (confidence interval) must be taken into account.

In all, 25,544 persons were selected to participate in the Canadian COVID-19 Antibody and Health Survey Follow-up Questionnaire (CCAHS-FQ).

Response Rate

In all, 25,544 persons were selected to participate in the CCAHS-FQ. The response rate to the electronic questionnaire was 41.1%.

Coverage Error

The CCAHS covers the population aged 18 and over living in the 10 provinces. Excluded from the survey's coverage are: persons living in the three territories; persons under the age of 18; persons living on reserves and other Indigenous settlements in the provinces; members of the Canadian Forces living on a base; persons living in institutions and residents of certain remote regions.

Non-sampling Error

Much time and effort was devoted to reducing non-sampling errors in the survey. Quality assurance measures were applied at each stage of the data collection and processing cycle to control the quality of the data.