2. Measuring disability at Statistics Canada A New Survey Measure of Disability: the Disability Screening Questions (DSQ)
2. Measuring disability at Statistics Canada

To put the DSQ in perspective, some background is necessary on how Statistics Canada has measured disability over the past 30 years.

2.1. Post-censal disability surveys

In May 1980, the Special Parliamentary Committee on the Disabled and the Handicapped was formed with the mandate to report to the House of Commons on the needs and concerns of persons with disabilities. In February 1981, the Committee published a report entitled Obstacles, which included 130 recommendations for action by the Government of Canada.

The lack of national data on persons with disabilities was noted. The Committee directed Statistics Canada, through Recommendation 113, “to give a high priority to the development and implementation of a long-term strategy which will generate comprehensive data on disabled persons in Canada . . . .”^{Note 1}

Statistics Canada responded with an action plan which outlined the major activities to be undertaken to build a national database that would include all types of disabilities and all geographic areas.

Representatives from federal, provincial and territorial departments, agencies, crown corporations, and associations of and for persons with a disability were contacted to determine their specific data requirements.

Statistics Canada undertook three major data collection activities:

1. The Canadian Health and Disability Survey (CHDS), which was a supplement to the Labour Force Survey in October 1983 and June 1984;
2. The addition of a question on activity limitation on the 1986 Census of Population questionnaire^{Note 2} to assist in designing a sample frame from which to select individuals for participation in the post-censal Health and Activity Limitation Survey (HALS); and
3. The HALS, which was completed for households in the fall of 1986, and for institutions in the spring of 1987. 

HALS, Statistics Canada’s first post-censal survey on disability, had a household and an institutional component, both of which covered children and adults in all provinces and territories.

The purpose of the question added to the 1986 Census long form was to identify a large part of the potential disabled population among those who had answered affirmatively to this filter question. Before the 1986 Census, a field test was conducted to determine if all disabled persons would answer affirmatively to the filter question; the results indicated that many people with a mild disability, as well as some of the elderly, would not do so. Of the individuals contacted for this field test, 5% had answered negatively to the filter question but were considered to have a disability (based on a longer set of screener questions).

For the household component of the 1986 HALS, the Census filter question was used to divide the population into two groups:  those who replied affirmatively to the filter question (the YES population), and the others (the NO population). To ensure complete coverage of PWD, a sample was taken from each population. The HALS was repeated after the 1991 Census, again with household and institutional components covering children and adults in all provinces and territories.

In 1996, the survey was cancelled owing to budget constraints. Although useful, the HALS was costly, with a sample size in households alone of close to 150,000.

In 2001, a new post-censal survey on disability replaced the household component of the HALS: the Participation and Activity Limitation Survey (PALS). A major change in survey design (with a notable impact on the coverage of PWD) was eliminating the NO population from the sample, thereby allowing for major savings and sample size reductions. The sample size was about 50,000 children and adults in the 10 provinces. The territories were dropped, as was the institutional component. However, to limit the impact of eliminating the NO sample,^{Note 3} new Census filter questions were developed—Activities of Daily Living (ADL) questions—for the 2001 Census long form. These questions were intended to cast the net more widely to better include false negatives who previously were captured only by the NO sample.

In 2006, the PALS was repeated (household component only), covering children and adults, and the territories were re-introduced.   

In 2012, a new “post-NHS”^{Note 4} survey replaced the PALS: the Canadian Survey on Disability (CSD). The design was similar to the PALS (covering only the YES population), but used a different definition of disability, requiring that a person reports activity limitations to identify a disability. The CSD did not include children younger than 15. As well, the CSD used the new Disability Screening Questions (DSQ), which are the main topic of this document.  

2.2. Other health measures

Other Statistics Canada surveys use different health-related questions. The DSQ are not meant to replace these measures, as each serves its own purpose. An overview of these measures is given here. The goal is to explain why they do not meet the needs addressed by the DSQ. This is by no means a criticism of these other measures, which have their own objectives and uses.   

2.2.1. The Health Utilities Index Mark 3 (HUI3)

The Health Utilities Index Mark 3 (HUI3), which was originally developed at McMaster University,^{Note 5} is a validated standardized measure used on an international basis to assess overall functional health based on eight attributes: vision, hearing, speech, ambulation, dexterity, emotion, cognition, and pain. Answers are combined into a scoring system that ranks respondents on a scale from -0.36 to 1, where higher numbers mean greater functional health. These questions have been used regularly on cycles of the Canadian Community Health Survey, the Canadian Health Measures Survey and were used extensively on the National Population Health Survey.

The HUI3 is not ideal as a proxy for disability. The major reason is conceptual—the HUI3 measures functional health, not disability. The disability module that was sought had to take into account activity limitations and use the International Classification of Functioning (ICF) framework.^{Note 6} HUI3 scores are primarily based on questions pertaining to “usual ability to perform selected tasks.” For example, people who indicate problems with particular tasks related to vision, hearing, speech, ambulation or dexterity can generate HUI3 scores that can lead to them being classified as having moderate or even severe conditions. However, under the social model and ICF framework, impairments and functional difficulties represent only one dimension of disability. The framework considers how those impairments/task difficulties interact with respondents’ environment and affect their ability to participate in and perform day-to-day activities. This can be achieved only through a second step that establishes if an impairment or task-based difficulty is accompanied by a limitation in daily activities.

As well, many people with severe disabilities see themselves as being in good health. Since the goal with the DSQ is to move toward the social model of disability and away from the medical model, this conceptual difference is problematic and results in the identification of somewhat different populations. Despite an expected overlap, a substantial percentage of the population identified by the HUI3 as having poor functional health would not likely be identified as having a disability under the social model. Similarly, the HUI3 would likely not identify a sizeable proportion of the people who would meet the criteria for the social model, particularly those with non-physical disabilities. The HUI3 and the social model of disability measure different things.

Another reason why the HUI3 is not ideal as a proxy for disability is that it does not adequately cover the mental health-related disabilities with its use of a "happiness scale". Although the HUI3 has a question about cognition, it combines several disability types. The module sought should, to overcome weaknesses in earlier modules, separately identify memory disabilities, learning disabilities, and intellectual or developmental disabilities (a core requirement for the disability community).

For mobility, the HUI3 focuses solely on walking. Work on the PALS to determine the minimum questions that must be asked to cover most people with potential mobility disabilities identified both walking and going up/down stairs as necessary. More important for DSQ purposes was the follow-up to determine if such difficulties limited daily activities. This is not covered by the HUI3.

Furthermore, past research using the PALS found that basic questions on task functioning often capture people with temporary problems. Disability, however, is long term, although it can be experienced on a cyclical/episodic basis. The DSQ development team sought to ensure that the sense of “long term” was incorporated in the new identification module and that it allowed for cyclical disabilities that occur episodically over a long period. The HUI3 does not accommodate these concerns.

Finally, the basic HUI3 does not meet the time requirements of the new module, which had to average less than 2 minutes to administer. An approach that was initially considered was to use the HUI3 (or a subset or variation) to identify impairments (conditions and task difficulty) and add follow-up questions about limitation of daily activities and about mental health-related disabilities and learning disabilities. However, the HUI3 (30 questions) was already too long for most general population surveys.

The HUI3 questions were initially used to devise wording for some questions of the new module (an effort was made to employ questions in use that had been tested if they could address DSQ needs), but the full HUI3 was not a good fit. Some portions of the HUI3 instrument were tested for use in the DSQ; those that tested poorly were abandoned.

2.2.2. The Washington Group set of questions

The Washington Group (WG) set of questions has been proposed as an international instrument to identify disability. The WG can be traced back to the United Nations International Seminar on Measurement of Disability in New York, June 4 to 6, 2001. Experts in disability measurement for statistical reporting from developed and developing countries reviewed methods currently used to measure disability in national statistical systems, with special attention to questionnaire design, and developed recommendations and priorities. Based on this meeting, the mandate for the WG was established. The first official meeting took place in Washington, D.C., February 18 to 20, 2002.

One of the purposes of the WG was to “identify all those at greater risk than the general population for limitations in participation.”^{Note 7} This is similar to the use of filter questions to develop a sample frame of people most likely to have a disability. However, like the HUI3, it does not go beyond detection of task difficulty/impairment element of disability, making the WG questions inadequate for DSQ purposes.

There are two sets of WG questions: the short set and the extended set. The extended set, which is still under development, exceeds the 2-minute time target. The short set concentrates on task difficulty using six questions pertaining to seeing, hearing, walking/climbing, remembering/concentrating, washing/dressing, and communicating. Like the HUI3, these questions do not cover the range of disability types required, notably, mental health-related disabilities and learning disabilities. As well, the short set of WG questions does not meet the requirement of including the impact of task difficulty.

Nonetheless, initial module designs for the DSQ attempted to use the WG questions to detect task difficulty/impairment. It was hoped that they could be augmented with follow-up questions to determine the degree of limitation caused by these difficulties/impairments. Some elements of these questions remain in the DSQ; others were abandoned or altered after qualitative testing.

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