Setting, design and data source
An online, cross-sectional survey of adults (≥ 18 years) residing in Canada was conducted by the Centre for Addiction and Mental Health in collaboration with the market research firm, Delvinia (see Table S1 in Additional File 1 for the Checklist for Reporting Results of Internet E-Surveys [CHERRIES]). The sampling frame was comprised of a million plus members of an existing web panel called AskingCanadians (see http://corporate.askingcanadians.com/ for further details on the web panel). The sampling methodology entailed quota sampling by age, gender and region (proportional to size of the population that spoke English). The survey was repeated at six time points since the pandemic began in 2020: Wave 1 (May 8 – May 12: N = 1,005; Completion Rate [CR] = 15.93%), Wave 2 (May 29 – June 01: N = 1,002; CR = 17.19%), Wave 3 (June 19 – June 23: N = 1,005; CR = 16.40%), Wave 4 (July 10 – July 14: N = 1,003; CR = 13.69%), Wave 5 (September 18 – September 22: N = 1,003; CR = 17.58%) and Wave 6 (November 27 – December 01: N = 1,003; CR = 16.22%) (see Table S2 in Additional File 1 for age, sex and regional compositions of the samples, as well as a comparison of the samples with the general population). Importantly, the sampling methodology ensured that participants were not included more than once in the survey (i.e. one-time inclusion in either of the six survey waves) due to the cross-sectional design. Further details regarding the survey methodology are described in the Supplementary Methods in Additional File 1.
Measurements
Daily cannabis use
Based on responses to the item “During the past seven days, on how many days did you use cannabis (also known as marijuana, hash, pot)?”, daily cannabis use (yes, no) was defined as cannabis use on at least five days during the past week.
Demographics
Demographics included gender (male, female), age (18 – 29 years, 30 – 39 years, 40 – 49 years, ≥ 50 years), region (Western [British Columbia, Yukon, Northwest Territories and Nunavut), Prairies [Alberta, Saskatchewan, Manitoba], Central [Ontario] and Atlantic [Quebec, New Brunswick, Newfoundland and Labrador, Nova Scotia, Prince Edward Island]), urbanicity (urban, suburban, rural), marital status (married or living with a partner, widowed, divorced or separated, never married), size of household (1 person, 2 people, 3 people, ≥ 4 people), ethnicity (white, non-white) and education (less than university or college completion, at least university or college completion).
Heavy episodic drinking
Heavy episodic drinking (yes, no) was defined as consumption of at least five drinks for men and at least four drinks for women in one drinking occasion during the past week.
Pandemic-related risks and impacts
Employment-related risk of contracting COVID-19 was determined by asking participants if they had a job that exposed them to a high risk of contracting COVID-19 (yes, no). Feelings of loneliness were measured by asking participants about the frequency of loneliness during the past week [15]: < 1 day, 1 – 2 days, 3 – 4 days and 5 – 7 days.
The impact of the pandemic on employment situation was determined by asking participants, “How have physical distancing measures due to the COVID-19 pandemic affected your employment situation?”, with the responses coded into six categories: currently working from home, currently not working or loss of employment, previously working from home during the pandemic, previously not working or loss of employment during the pandemic, other and no change. The impact of the pandemic on financial situation was examined by asking participants, “How worried are you about the impact of COVID-19 on your personal financial situation”: not at all worried, not very worried, somewhat worried and very worried.
Statistical analysis
To maximize the sample size for the statistical analyses, adjacent survey waves were collapsed into periods: Period 1 (Waves 1 – 2), Period 2 (Waves 3 – 4) and Period 3 (Waves 5 – 6). Trends in daily cannabis use in the overall sample were examined using the Cochran-Armitage test. This analysis was then repeated among the various population subgroups to test for differential patterns of change. The examined population subgroups included categories of gender, age, region, urbanicity, marital status, ethnicity, education and heavy episodic drinking. Given the number of simultaneous tests performed, adjustments were made for multiple comparisons using the Bonferroni Correction, a conservative approach that focuses on large and meaningful changes. Thereafter, risk characteristics associated with daily cannabis use were identified using cross-tabulations with chi-square tests. Risk characteristics with p < 0.05 in these analyses were subsequently entered in multivariable logistic regression analyses. Variance inflation factors were generated to assess multicollinearity and the Hosmer–Lemeshow test was used to assess the model fit.