Childhood National Immunization Coverage Survey (CNICS)

Detailed information for 2015

Status:

Active

Frequency:

Every 2 years

Record number:

5185

The purpose of the Childhood National Immunization Coverage Survey is to collect information on national immunization coverage for childhood vaccines.

Data release - June 28, 2017

Description

The purpose of the Childhood National Immunization Coverage Survey (CNICS) is to collect information on national immunization coverage for childhood vaccines. The survey is intended to:

- Determine if children are immunized in accordance with recommended immunization schedules for publicly-funded vaccines
- Provide the World Health Organization and the Pan American Health Organization with estimates of national immunization coverage for diphtheria-pertussis-tetanus (DPT) and for measles-mumps-rubella (MMR) and other vaccines for children
- Assess parental knowledge, attitudes, and awareness of vaccines.

Reference period: Varies

Collection period: From fall to spring

Subjects

  • Children and youth
  • Health

Data sources and methodology

Target population

The target population for this survey is boys and girls aged 2, 7 and 17 years old, and girls aged 13-14 years old on March 1st, 2015, living in the 10 provinces and three territories, not residing on Indian reserves.

Instrument design

The content of the original 2011 cycle was developed in coordination with the Public Health Agency (PHAC). The survey content was tested by the Questionnaire Design Research Centre of Statistics Canada in one-on-one interviews in participants' homes prior to collection. There were no significant content changes in 2011 and 2013.

Data collection for the CNICS is comprised of three components. The first component is a computer assisted telephone interview (CATI) during which the parent answers survey questions about their child's immunizations. The completion of the telephone interview triggers the second component, a mail out/mail back Parent Consent form, which is sent to respondents who agreed at the time of the interview to give written consent to Statistics Canada to contact their immunization provider(s). The third component is the Immunization Record Request form, a mail out/mail back questionnaire sent to the child's immunization provider(s) who fills it out with the child's immunization history (name of vaccination and date given). The data provided by the immunization providers are used to enhance the parent reported data.

Sampling

This is a sample survey with a cross-sectional design.

The main objective of the 2015 CNICS is to produce national estimates of coverage for childhood vaccines for boys and girls aged 2, 7 and 17 years old, and girls aged 13-14 years old. The target population is stratified by age and by province and territory to ensure that the sample is representative while remaining efficient. It was determined that a sample of 3,139 units would yield the desired accuracy.

Data sources

Data collection for this reference period: 2015-10-05 to 2016-04-30

Responding to this survey is voluntary.

Data are collected directly from survey respondents.

Data collection for the Childhood National Coverage Survey was comprised of three components. The first component was a computer assisted telephone interview (CATI) during which the parent or guardian (the person most knowledgeable or PMK) answered survey questions about their child's immunizations. The completion of the telephone interview triggered the second component, the mail out/mail back Parent Consent Form, which was sent to respondents who agreed at the time of the interview to give written consent to Statistics Canada to contact their health care provider(s). The third component was the Immunization Record Request Form; a mail out/mail back questionnaire sent to the child's health care
providers) who then filled it out with the child's immunization history (name of vaccination and date given).

Collection for the CATI component of the CNICS took place between October 2015 and January, 2016. Two regional offices, Halifax, and Edmonton conducted the interviews. Two weeks before data collection started, an introductory letter was mailed to the potential PMK of the selected child. The letter informed respondents of the purpose of the voluntary survey and requested they have their child's immunization records available during the interview. Data on immunizations were collected if respondents had an immunization record on hand at the time of the interview. Otherwise, the immunization questions were skipped and respondents were asked about their knowledge, attitudes and beliefs about immunizations.

To maximize response rates, the regional offices used a tracking system for non-response follow-up. In cases where the Parent Consent Form or Immunization Record Request Form was not returned after two weeks of being mailed out, interviewers would make follow-up calls to remind respondents to return the form at the earliest possible convenience.

Immunization data are collected from the parent or guardian of the selected child and the child's health care provider(s). The data from both sources, when available, were used to estimate immunization coverage. The data reported by the parent/guardian were combined into a single record and sorted chronologically for each vaccine given. Each vaccine had to be at least 28 days apart to be considered valid. When there were discrepancies between the dates reported by the parent or the health care provider(s), the date(s) provided by the health care provider(s) generally took precedence.

Error detection

The purpose of processing survey data is to adapt the collected data into a form that is appropriate for analysis and tabulation.

For the CNICS, collection was performed using a Computer Assisted Telephone Interview (CATI), which allows for certain edits to be built into the application. For example, Validity Edits, which ensure that the response falls within the allowed range. It also ensured that only character values were entered into character fields or numeric values were entered into numeric fields.

After collection the raw data file was put through a series of standard processing steps designed to clean the data and help ensure its consistency thereby increasing its usefulness. The edits were done on the data both at the micro and macro level.
The flow edits replicated the flow patterns used in the application and set the non-applicable questions to a value of 'Valid Skip'. Non-responses were set to a value of 'Not Stated'. These are questions that were applicable to the respondent but were not answered. In a CATI application these value usually follow a response of 'Refusal' or 'Don't Know'.

In addition, various types of editing were done to detect missing or inconsistent information. For example, edits were performed to check the logical relationship between responses.

New variables were derived using collected variables. A derived variable may be based on one variable by re-grouping or collapsing the categories or based on several variables, by combining them together to define a new concept.

Imputation

Total household income was imputed. An imputation flag has been included on the CNICS file so that users will have information on the extent of imputation.

Income imputation was done using trend imputation method, based on the CCTB income. With this method, the observed trend of the donor multiplied by the CCTB receiver income must fall within the range provided by the receiver, when available. The donor's trend is calculated as the ratio of its income, as reported to CNICS, over its CCTB income. When no range is specified, the method relies more heavily on the CCTB income. The following rule must be respected : the CCTB income from the donor and from the receiver must not differ too much. Trend imputation is done by groups using the following information: province, presence of a spouse and number of persons aged 15 and over (other than the parents) in the household.

For the cases where it is impossible to apply the method, because the receiver CCTB income is not available, income imputation was done using the nearest-neighbour imputation method. The first step of this method is to find a respondent (the donor) who answered the income section and has characteristics similar to those of the respondent who did not provide complete income information (the recipient). The donor's record is then used to calculate the values to be imputed to the recipient's record.

Estimation

The Childhood National Immunization Coverage Survey (CNICS) is a probability survey. As is the case with any probability survey, the sample is selected so as to be able to produce estimates for a reference population. Therefore, each unit in the sample represents a number of units in the population.

Survey weights are calculated by taking the child's design weight and making adjustments for survey non-response and post-stratification to ensure that the final survey weights sum to known counts of children by age. The design weight is the inverse of the probability of selection, that is, the probability that a child in the population is selected into the CNICS sample.

First adjustment: Non-response adjustment
We needed to adjust the weights so that the respondents represent the non-respondents. Otherwise, we would, for example, underestimate totals. To decide how to assign the weight of the non-respondents to the respondents, we apply the method of response homogeneous groups (RHGs). The RHG method involves grouping individuals with the same likelihood of response. Then an adjustment factor is computed for each RHG. In the first step, the weights of the cases that we were not able to contact were given to cases for which a contact was made (respondents and other non-respondents) while with the second step, the weights of the other non-respondents were given to the respondents.

Second adjustment: Post-stratification
The last adjustment factor ensures consistency between the estimates produced by CNICS and Statistics Canada's population estimates by age and province. This method is called post-stratification. The purpose of this adjustment is to ensure that the sum of the weights match known population totals

Numbers used in the post-stratification refer to the population counts on March 1st, 2015, as estimated by Statistics Canada.

Because of a high percentage of partial non-response for a component of the survey, two weights were calculated for CNICS. The first weight can be used to estimate the coverage for all vaccines while the other weight can be used to assess knowledge, attitudes and awareness of vaccines. Both weights were calculated using the aforementioned methodology.

Sampling variance calculation

It would be difficult (not to say impossible) to derive an exact formula to calculate the sampling variance for CNICS because of the sample design, non-response adjustments, treatment of out-of-scope units and post-stratification. Actually, such a task could only be undertaken under such strong assumptions as to yield a framework too simplistic to be of any use in practice. One way to approximate the sampling variance is to use the bootstrap method. With that method, we generate a set of 1,000 weights, known as bootstrap weights, which are derived from the survey weights and used to estimate the variance of the estimates. Two sets of 1,000 bootstrap weights are available for CNICS on a separate data file.

Quality evaluation

While rigorous quality assurance mechanisms are applied across all steps of the statistical process, validation and scrutiny of the data by statisticians are the ultimate quality checks prior to dissemination. Many validation measures were implemented. They include:
a) Analysis of changes over time
b) Verification of estimates through cross-tabulations
c) Consultation with stakeholders internal to Statistics Canada
d) Consultation with the Public Health Agency of Canada
e) Review of production processes
f) Coherence analysis based on quality indicators

Disclosure control

Statistics Canada is prohibited by law from releasing any data which would divulge information obtained under the Statistics Act that relates to any identifiable person, business or organization without the prior knowledge or the consent in writing of that person, business or organization. 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.

In order to keep the data confidential, some modifications are performed on the collected data. For example, the survey questionnaire asked for the country of origin of the child and parents; however, only the continent of origin is available on the microdata file.

Revisions and seasonal adjustment

This methodology does not apply to this survey program.

Data accuracy

For the CNICS, coverage is defined as those who had the required number of doses of each vaccine by a specific age. For example, children must have four doses of diphtheria, pertussis, and tetanus by their second birthday to meet the coverage requirements for those immunizations. The coverage estimates and the confidence intervals for two-year-old children on the 2015 CNICS are provided in the additional document link below.

Date modified: