Friday 6 January 2017

How many Canadians smoke pot ? Depends on who is asking

Making evidence informed policy for marijuana will rely on the availability of evidence - and that  includes having a good handle on how many Canadians are using this dependence-producing drug.

It would appear that usually reliable research methods are get conflicting results on the prevalence of marijuana use. Take, for example, three recent surveys of marijuana use by respected organizations.
  • The Canadian Tobacco, Alcohol and Drugs Survey, which is managed by Health Canada and which questioned 15,000 Canadians 15 years and older in 2015 with a participation rate of 58%. The questions asked were "During the past 12 months have you used marijuana?
    During the past three months have you used marijuana? During the past three months how often did you use marijuana?"
    The results would have included both recreational and medical use.
  • A survey by Ekos Canada, commissioned by Health Canada and released under the (very helfpul) guidelines on release of public opinion research. It surveyed 2,201 Canadians 13 years of age and over in May and June 2016, with a participation rate of 20%. The questions asked were: "Have you used marijuana in the past 12 months?"/ "Over the past 12 months, how often have you used marijuana on average?" "When legalized in Canada how likely would you be to use/try marijuana?"The results would have included both recreational and medical use.
  • The third is a business-oriented report by Deloitte and Riwi Corp, which surveyed 5,000 Canadians aged 19 and over in March-April 2016. The participation rate was not stated and the questionnaire has not been located. The results state that medical use of marijuana was excluded.
The results, as shown below, give very different pictures of the situation.


CTADS
EKOS
DELOITTE
Age:
15 +
13 +
19 +
Sample size
15,000
2,200
5,000
Survey period
 2015
 Summer 2016
 Spring 2016
Past year use or occasional use
12 %
(incl. medical)
38%
(incl. medical)
22%
(excl. medical)
Daily use
2.8%
8.4%
7%
Might use if it were legalized (but don’t currently use)
 n/a
14%
17%