The data

Data source

This study is based on data from the Neurological Conditions Prevalence File, which was derived from the 2010 and 2011 Canadian Community Health Survey–Annual Component (CCHS), and the 2011 Survey of Living with Neurological Conditions in Canada (SLNCC). Documentation for these surveys is available at www.statcan.gc.ca.

The CCHS is a cross-sectional survey that collects information about health status, determinants of health, and health care use for people aged 12 or older living in private households. The sampling frame excludes full-time members of the Canadian Forces, the institutionalized population, and people living in some remote areas and on reserves and other Aboriginal settlements in the provinces. The Neurological Conditions module captured information on all household members, including children. Respondents who agreed to share their data with the survey’s share partners—the Public Health Agency of Canada, Health Canada, provincial ministries of health, Institut de la Statistique du Quebec (respondents living in Québec)—were included in the Neurological Conditions Prevalence File, which had a sample size of 285,971, with a response rate of 70.6%.

The SLNCC is a cross-sectional survey designed to explore issues related to neurological conditions among people aged 15 or older living in private households. In addition to the groups routinely excluded from the CCHS, the SLNCC excluded residents of the three territories.  The SLNCC sample was composed of 4,569 respondents for a response rate of 81.6%. This study uses a subsample of 372 (295 females, 77 males) with migraine but none of the other neurological conditions included on the survey. They represent an estimated 970,000 Canadians, 84.2% of whom were female, with an average age of 42.6 years.

Definitions

Respondents to the CCHS were asked to report on selected neurological conditions that had lasted or were expected to last six months or more and had been diagnosed by a health professional (Appendix B).

Additional questions in the SLNCC referred to the past 12 months.Note16,Note17 Those with positive responses to at least two of the three follow-up questions were categorized as having “current” migraine:

Did you have a headache where you felt nauseated or sick to your stomach?
Did light bother you when you had a headache (a lot more than when you did not have a headache)?
Did your headache limit your ability to work, study or do what you needed to do for at least a day?

Scores on the 9-item Patient Health Questionnaire (PHQ-9)Note18 were used to classify depression: no depression (0), minimal/mild (1 to 9), or moderate/moderately severe /severe (10 to 27).

Respondents were asked if they had taken prescription medication in the past three months for their neurological condition. They were instructed to include non-prescription medication if it had been prescribed by a health professional. Those who responded “no” were asked to indicate all reasons that applied for not taking prescription medication. Responses of “side effects caused by medication,” “medication not working,” “ran out of medication,” “too costly/financial constraints” or “other” were combined because of small sample size.

Questions about out-of-pocket expenses referred to prescription and non-prescription medications related to their neurological condition that would not be reimbursed by insurance or government programs. The reference period was the past 12 months.

Responses to the question, “Overall, how much do you feel that your neurological condition(s) affects your life?”, were categorized as “not at all” or “a little bit” versus “moderately”, “quite a bit” or “extremely.”

Respondents who answered “no” to the question, “Are you usually free of pain or discomfort?”, were asked how many activities their pain prevents. Those who responded “a few,”“some” or “most” (versus “none”) were considered to have pain that prevents activities.

Respondents who reported that because of their neurological condition they felt left out of things “sometimes,” “often” or “always” were grouped versus those who responded “never” or “rarely.”

Respondents older than 16 who had a valid driver’s licence were asked if their neurological condition had ever prevented them from driving, even for a short time.

Responses to the question, “How much do you feel that your condition has limited you in getting a good night’s sleep?” were grouped into three categories: “not at all,” “a little bit/moderately,” or “quite a bit/extremely.”

Based on their employment status in the week before the interview, respondents were classified as currently working if they had worked at a job or business or been absent from work; did not have a job last week; or permanently unable to work. Respondents older than age 75 were excluded.

Changed work activities indicates whether respondents who had previously been employed  had ever changed their work activities for a at least three months because of their neurological condition, such as reducing hours, changing the type of work, or stopping work altogether.

Currently employed respondents younger than 76 were asked, “In the past three months, how many days of work have you missed because of your condition(s)?”

Socio-demographic variables included in the analysis were sex, age, and province or territory of residence.

Weighted frequencies, cross-tabulations and means were used to examine the prevalence of migraine in Canada and its impact on migraineurs. To account for survey design effects, standard errors and coefficients of variation were estimated using the bootstrap technique.Note19,Note20

Limitations

The criteria for identifying migraineurs differ between the CCHS and the SLNCC. In the CCHS, which was used for prevalence estimates, respondents were classified as migraineurs if they reported that their condition had been diagnosed by a health professional. This differs from the ICHD criteria, which are considered the gold standard (Appendix Table A). Consequently, the prevalence of migraine in this study is likely an underestimate, as it is influenced by factors such as access to health care and the decision to seek care. The SLNCC, which was used to study the impact of migraine, contains additional criteria that have been shown to be a good replacement for the full ICHD criteria.Note16,Note17 However, in the SLNCC, respondents were also instructed to report diagnosed migraine.

All neurological conditions were self-reported and not verified by another source. It is not possible to differentiate between primary headaches and those resulting from other disorders or between the major migraine subtypes—with or without aura.

Chronic and episodic migraine are not distinguished, the former being associated with greater disability.Note6,Note21

Without a specified period, the CCHS migraine question likely captures a mix of lifetime and current migraine. The additional questions in the SLNCC refer to the past 12 months; therefore, the analysis of associations between migraine and other factors pertains to the population with “current” migraine.

Questions about medication use specified “prescribed” medications, which could include over-the-counter drugs only if they had been prescribed by a health professional. On the other hand, when asked about out-of-pocket expenses, respondents were instructed to report prescription and non-prescription medications. Thus, the medications being considered may differ when respondents report on “use” versus “expenses.”

The study pertains to people living in private households and does not represent residents of health care institutions. Information about children younger than 12 is limited to prevalence estimates. Migraine-specific questions, such as medication use, age of onset/diagnosis and impacts, were asked on the SLNCC, which has a minimum age of 15.

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