The Canadian Health Measures Survey (CHMS) aims to collect important health information through a household interview and direct physical measures at a mobile examination centre (MEC), sometimes referred to as a mobile clinic.
Data release – September 20, 2012 (first in a series of releases). Please refer to the left sidebar, under the heading "The Daily".
The Canadian Health Measures Survey (CHMS), launched in 2007, is collecting key information relevant to the health of Canadians by means of direct physical measurements such as blood pressure, height, weight and physical fitness. In addition, the survey is collecting blood and urine samples to test for chronic and infectious diseases, nutrition and environment markers.
Through household interviews, the CHMS is gathering information related to nutrition, smoking habits, alcohol use, medical history, current health status, sexual behaviour, lifestyle and physical activity, the environment and housing characteristics, as well as demographic and socioeconomic variables.
All of this valuable information will create national baseline data on the extent of such major health concerns as obesity, hypertension, cardiovascular disease, exposure to infectious diseases, and exposure to environmental contaminants. In addition, the survey will provide clues about illness and the extent to which many diseases may be undiagnosed among Canadians. The CHMS will enable us to determine relationships between disease risk factors and health status, and to explore emerging public health issues.
CHMS data are representative of the population whether they are healthy or not and provide a better picture of the actual health of Canadians.
The following are some of the measures that the CHMS includes:
. Anthropometry (standing height, sitting height, weight, waist circumference, hip circumference, neck circumference, skinfolds)
. Cardiovascular health and fitness (blood pressure, modified Canadian Aerobic Fitness Test)
. Musculoskeletal fitness (hand grip strength, sit and reach test, partial curl-ups)
. Physical activity (accelerometry)
. Lung health (spirometry)
. Nutritional status (e.g., folate, Vitamin D)
. Diabetes (e.g., glycated hemoglobin)
. Cardiovascular health (e.g., lipid profile)
. Environmental exposure (e.g., lead, mercury)
. Infection markers (e.g., hepatitis)
. Kidney health (e.g., microalbumin, creatinine)
. Environmental exposure (e.g., cotinine, pesticides)
. Nutritional status (e.g., iodine)
Indoor air measures (household)
. Environmental exposure (volatile organic compounds)
The CHMS stores biological samples for further analyses of measures at a later date. The CHMS team works closely with the Health Canada and Public Health Agency of Canada Research Ethics Board and the Office of the Privacy Commissioner of Canada in order to address privacy issues and to implement proper laboratory procedures.
The CHMS covers the population 3 to 79 years of age living in the ten provinces and the three territories. Excluded from the survey's coverage are: persons living on reserves and other Aboriginal settlements in the provinces; full-time members of the Canadian Forces; the institutionalized population and residents of certain remote regions. Altogether these exclusions represent less than 4% of the target population.
Household Questionnaire Design
The CHMS household questionnaire was conceived in collaboration with specialists from Statistics Canada, Health Canada, the Public Health Agency of Canada and specialists in medical and academic fields. The CHMS questions were designed for computer-assisted personal interviewing (CAPI), meaning that, as the questions were developed, the associated logical flow into and out of the questions was programmed. This included specifying the type of answer required, the minimum and maximum values, on-line edits associated with the question and what to do in case of item non-response.
Each question had to relate to a physical measure. Experts thoroughly reviewed the questionnaire many times during development. They provided valuable feedback on the questions and on the related physical measures.
The CHMS questionnaire and collection application were qualitatively tested to ensure respondent understanding of the questions and to identify any errors.
This is a sample survey with a cross-sectional design.
The sample was allocated over 11 age-gender groups, with between 500 to 600 units per group (5,700 total) required to produce national estimates.
Since reporting units had to get to a mobile examination centre (MEC) located near their home for the physical measurements, site areas were limited to a radius of about 50 km (or up to 100 km for rural areas). To achieve this, collection sites were created using the Labour Force Survey's (LFS) area frame. The LFS geographic units used to define the sites were also grouped with respect to provincial and census metropolitan-area boundaries and population density criteria.
Using this frame, 257 sites were created, including 2 sites in the Territories. These sites were stratified based on the five regions of Canada: Atlantic, Quebec, Ontario, Prairies (including Yellowknife) and British Columbia (including Whitehorse). It was decided that a sample of 18 collection sites was required. These sites were allocated by region: Atlantic (2), Quebec (4), Ontario (6), Prairies (3) and British Columbia (3).
Within each region, sites were sorted according to the size of their population and whether or not they belonged to a census metropolitan area. Sites were randomly selected using a systematic sampling method with probability proportional to the size of each site's population.
Approximately 350 reporting units per site participated in all parts of the survey, with a total of 6,400 across all sites.
Within each of the 18 selected sites, the list of the Census 2006 dwellings were used as a frame. New dwellings from Statistics Canada's address register were also used to improve the frame coverage.
Using the date of birth of household members present at Census time, as well as more current information from other administrative sources, dwellings were stratified according to six age groups. The sample was allocated in each stratum in such a manner as to obtain the target number of respondents by age group.
Selected dwellings were asked for the household member list at the time of the survey and one or two persons per household were selected to participate in the survey. The selection of persons was done randomly using a vector with variable selection probabilities by age group.
Data collection for this reference period: 2009-08-27 – 2011-11-30
Responding to this survey is voluntary.
Data are collected directly from survey respondents.
Collection included a combination of a personal interview using a computer-assisted interviewing method and, for the physical measures, a visit to a mobile examination centre (MEC) specifically designed for the survey.
The CHMS collected data in 18 sites across the country. The collection sites were located in seven provinces: Newfoundland and Labrador, Nova Scotia, Quebec, Ontario, Manitoba, Alberta and British Columbia. Collection was scheduled so that each region was distributed within the two-year collection period, distributed between seasons and in a way that tried to minimize the movement of staff and equipment between sites. The CHMS MEC stayed in each site for five to seven weeks, collecting direct measures from approximately 350 respondents per site.
First step: personal interview at the household
The first contact with respondents was a letter sent through the mail. The letter informed people living at the sampled address that an interviewer would visit their home to collect some information about the household.
At the home, the application randomly selected one or two respondents and the interviewer conducted a separate health interview with each of them. The interview took 45 to 60 minutes per respondent. The interviewer then assisted the respondent in setting an appointment for the physical measures at the CHMS MEC.
Second step: visit to the CHMS MEC
Statistics Canada uses MECs to conduct the physical measures portion of the survey. Similar MECs have been used successfully for years by the NHANES in the United States.
The MEC consists of two trailers linked by an enclosed pedestrian walkway. One trailer serves as a reception and administration area, while the other contains physical measure rooms and a laboratory.
For each respondent, the complete visit to the MEC lasted about two hours. This is an approximate time, given that each respondent was assessed for their suitability for each measure and tested accordingly.
For children under 14 years of age, a parent or legal guardian had to be present with the child at the MEC and had to provide written consent for the child to participate in the tests.
At the end of their visit to the MEC, respondents were provided with a waterproof activity monitor. This small device was worn for a week at all times except when sleeping - even when swimming or bathing. It records information about normal physical activity patterns without the respondents having to do anything special.
Respondents were also asked to place an indoor air sampler, a small cylindrical device, in their home for the week following their visit to the MEC. The sampler measures a number of airborne substances in order to establish national baselines for indoor air concentrations of over 80 different volatile organic compounds.
Edits were developed as part of the data capture application. These edits, including range checks and cross-references, are applied at the time of collection to ensure data quality. Anomalies in the information reported are confirmed with the respondent right away and corrected if necessary.
For the computer-assisted personal interviewing (CAPI) application, it is not possible for interviewers to enter out-of-range values, and flow errors are controlled through programmed skip patterns. For example, CAPI ensures that questions that do not apply to the respondent are not asked. In response to certain types of inconsistent or unusual reporting, warning messages are invoked. In some instances, no corrective action is taken at the time of the interview and edits are instead performed at Head Office after data collection.
Income data are imputed due to a high percentage of missing values.
A survey weight is given to each person included in the final sample, that is, the sample of persons having answered the survey. This weight corresponds to the number of persons represented by the respondent for the entire population. When an estimate is produced, the survey weight must be used to ensure the estimate represents the population. If the survey weight is not used, the estimate represents only the sample.
In order to determine the quality of an estimate using the coefficient of variation (CV) (see the Data accuracy section) or to calculate confidence intervals, the standard error of the estimate must be calculated. The standard error is the square root of the sampling variance. Since the CHMS uses a multi-stage survey design, there is no simple formula that can be used to calculate sampling variance. Instead, the bootstrap re-sampling method is used to take into account the sample design information and to easily obtain variance estimates. This method selects in each stratum, a simple random sample of (n-1) of the n first stage sampling units selected with replacement to form a replicate. In each replicate, the survey weight for each record in the (n-1) selected first stage sampling units is recalculated. These weights are then post-stratified according to demographic information in the same way as the survey weights in order to obtain the final bootstrap weights. This process is repeated 500 times for the CHMS.
Several commercial software programs are available that can use these bootstrap weights to calculate the sampling variance estimates and standard errors. Statistics Canada has also developed a program that can perform all of these calculations for the user: the Bootvar program.
Household data quality protocols
To reduce the number of non-response cases and to ensure that procedures are followed consistently, the interviewers are all extensively trained by Statistics Canada, provided with detailed interviewer manuals, and are subject to regular observations. Refusals are followed up by an interviewer manager to encourage respondents to participate in the survey. Total non-response is handled by adjusting the weight of households that responded to the survey to compensate for those who do not respond.
Mobile examination centre (MEC) and lab data quality protocols
At the end of the household interview, the interviewer provided the respondent with guidelines specific to the appointment time slot for which they were randomly selected (AM or PM/evening). The guidelines serve to ensure standardization by minimizing the potential factors that will affect the results of certain tests, thus enhancing the quality of the data collected. At the beginning of the MEC visit, adherence to these guidelines was verified and documented.
Staff were selected based on the level of education, experience and certification(s) required for each field staff position. In addition, a significant amount of survey-specific training was provided to all field staff, emphasizing quality control guidelines and the need for standardization of all survey procedures. Replicate testing (QC sampling) was done regularly at the MEC on the anthropometry component. Replicate lab samples and commercial control samples were sent to the CHMS external labs to assess the accuracy and precision of laboratory testing. Field blanks were also sent to the CHMS external labs to ensure that samples were not being contaminated by the MEC environment and processes.
Observations of all MEC staff were performed at regular intervals to provide a direct evaluation of protocol adherence, interaction with respondents and overall data collection quality and functioning of the MEC. In some cases, content-specific experts were involved in both observations of MEC staff and data reviews (e.g. spirometry).
Data validation was performed halfway through cycle 2 data collection and at the end of cycle 2 data collection in order to ensure that the data were complete and accurate. Cycle 2 CHMS household, MEC and laboratory data were compared with cycle 1 CHMS, Canadian Community Health Survey and American data (e.g. National Health and Nutrition Examination Survey) to ensure that the data were consistent between these different data sources. Additional work was done to validate certain household data against comparable directly-measured MEC data.
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.
Considerable efforts have been taken to ensure high standards throughout all stages of collection and processing. However, the resulting estimates are inevitably subject to a certain degree of non-sampling error. Non-sampling error is not related to sampling and may occur for various reasons. Non-response, population coverage, differences in the interpretations of questions and mistakes in recording, coding and processing data are other examples of non-sampling errors.
Total non-response is handled by adjusting the weight of persons in households that responded to the survey to compensate for those who do not respond.
Sampling error can be measured by the standard error (or standard deviation). The coefficient of variation (CV) is the standard error expressed as a percentage of the survey estimate and is used to qualify its quality. Estimates with smaller CVs are more reliable than estimates with larger CVs.