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Estimation of Voter Turnout by Age Group and Gender at the 2011 Federal General Election

Appendix: Methodology

The purpose of the study was to estimate voter turnout rates for several demographic groups of interest defined by province or territory, age, and sex.

Definition of Turnout

The official turnout results published by Canada's Chief Electoral Officer are calculated using the number of registered electors in the denominator instead of the size of the electoral population. This introduces bias into the turnout results, especially when broken down by age or when making comparisons over time, for at least three reasons:

  1. Younger age groups are less likely to be registered as electors for a variety of reasons, including lack of interest or initiative and high mobility rates.
  2. The coverage of the electoral list (that is, the percentage of eligible electors listed) changes over time, depending on many factors related to list maintenance activities, among other things. If turnout is calculated relative to the number of electors on the list, then measures of change in turnout over time will be confounded by these other factors. This problem is exacerbated when turnout is broken down by age, since the changes in coverage over time may be quite different for different age groups. For example, an apparent decrease in youth turnout may be partly due to Elections Canada's efforts to increase coverage of youth on the list.
  3. Many electors only get registered when they go to vote. Therefore, non-voters are slightly under-represented on the list of electors, making turnout appear artificially higher. This problem too is exacerbated when turnout is broken down by age, since the youngest age groups also tend to be the ones most likely to get registered when they go to vote.

As for previous studies, turnout is defined as the number of ballots cast divided by the size of Canadian population eligible to vote. The denominator is calculated by adjusting population estimates obtained from Statistics Canada to include only citizens over 18 years of age as of Polling Day (May 2, 2011). In order to get the numerator, we need to know who cast a ballot and what group they fall into. This was obtained for a sample of electors, which was used to produce an estimate of the numerator for each demographic group of interest.

Electoral Population

The size of the electoral population within a demographic group of interest is required for the denominator of the turnout estimates. This was based on Statistics Canada's 2006 Census, with adjustments made to remove non-citizens and those under 18 years of age, who are not eligible to vote. Additional adjustments were made to take into account population growth during the time elapsed between Census Day and Polling Day, using demographic information provided by Statistics Canada and Citizenship and Immigration Canada. The population estimates used for this study can be found on Elections Canada's website at www.elections.ca/res/rec/part/estim/41st_GE_turnout_e.xlsx.

Definition of Age Groups

For the purposes of this study, age as of Polling Day was divided into eight groups, which was consistent with previous studies. The groups were defined as follows:

Table 2: Age Group Definition (2011 Federal General Election)
Age group From To
1st time Oct 15, 1990 May 2, 1993
not 1st time May 3, 1986 Oct 14, 1990
2534 May 3, 1976 May 2, 1986
3544 May 3, 1966 May 2, 1976
4554 May 3, 1956 May 2, 1966
5564 May 3, 1946 May 2, 1956
6574 May 3, 1936 May 2, 1946
75+ - May 2, 1936

Youth aged 1824 were split into two groups: those who were eligible to vote for the first time in the 2011 federal general election and those who were eligible to vote in the 2008 federal general election.

Sample Design

Elections Canada maintains administrative records that contain address, date of birth and gender for everyone on the final voters list. They do not indicate which electors cast ballots, except in special circumstances. The administrative data can be used to identify all those who voted at advance polls, by special ballot, or who registered to vote on Polling Day. For those who voted on Polling Day but were registered earlier, the information required is only available on the strike lists used to administer the election.

The information on the strike lists is currently not captured electronically. It would be prohibitively expensive and time-consuming to obtain them all from each polling station and capture the required information after the fact. Instead, a relatively small random sample of 1,800 polls was selected and the strike list from each selected poll was obtained. The information required was then captured, and an estimate of the number of votes cast by regular ballot on Polling Day by non-registering electors was produced for each demographic group of interest. The final estimates required for the numerator of turnout were then produced by adding these estimates to the known numbers of ballots cast in each group at advance polls, by special ballot, and by those who registered to vote on Polling Day.

Based on previous studies and practical considerations of time and resources, an overall sample size of 1,800 polls was determined to be sufficient to produce estimates with acceptable margins of error at the provincial or territorial level.

For practical reasons related to how the strike lists are stored following the election, the sampling was carried out in two stages. In the first stage, 60 electoral districts were selected at random from the 308 across Canada. In the second stage, 30 polling stations were selected from each of the 60 selected electoral districts, yielding an overall sample size of 1,800 polling stations. At both stages, strata based on the age distribution of registered electors were used to ensure sufficient coverage by the demographic groups of interest.

Margins of Error for Turnout Estimates

Margins of error for the estimates were obtained by producing 95% confidence intervals around the estimates, using the calculated standard errors and assuming a normal sampling distribution. For the 2011 general election, this sampling and estimation methodology produced estimates of voter turnout by age group with margins of error between 1 and 2 percentage points at the Canada level and between 3 and 9 percentage points at the provincial or territorial level, for almost all age groups. Actual participation rates should be within the associated margin of error for the estimates 19 times out of 20.

Throughout this document, a difference was said to be statistically significant at the 5% error level if the estimated difference was larger than the associated margin of error.

Tables showing the statistical margins of error by province or territory, age group, and gender are provided on Elections Canada's website at www.elections.ca/res/rec/part/estim/41st_GE_turnout_e.xlsx.

Post-Stratification of Turnout Estimates

Because the numerators used in the turnout estimates were estimated from a sample, there would be a margin of error associated with each, and they would therefore not add up across demographic groups to the official number of ballots cast within a province or territory. To account for this, the numerator estimates were therefore adjusted to agree with the known totals at the province or territory level, using a statistical procedure called post-stratification. Because of the post-stratification adjustment, there is no margin of error for the total estimates across all age or gender groups at the province or territory level. That is, the adjustment ensures that the estimates agree exactly with the known values at this level.