Study results suggest that anti-smoking legislation appears to play an important role in decreasing SHS exposure. Overall, smoking bans appear most effective in decreasing exposure to SHS in public places. They also appear to increase the prevalence of complete smoking restrictions at work. But they appear to have additional benefits by decreasing the percentage of current smokers and decreasing exposures to SHS in private settings (cars and homes). Overall, municipalities with full smoking bans had lower reported SHS exposure in public places and a greater prevalence of complete smoking restriction at work than in areas with partial bans. SHS exposure is related to the level of restrictions municipalities place on banning smoking in different locations. Our results are consistent with other cross-sectional surveys conducted before and after the implementation of smoking bans. Two cross-sectional studies conducted in Scotland before and after the introduction of a statewide smoking ban are in agreement with our results even though they measured salivary continine , , ).
Approximately one-third of respondents in 2005 still reported smoking exposure at home. This number is higher than percentages of people exposed in the European Union and the United States , . Studies have also shown that smoking employees are also affected by these bans by decreasing cigarette consumption, increasing smokers' desire to stop. Our results are consistent with a systematic review in which smoke-free workplaces were associated with a decrease in smoking prevalence of 4% .
The prevalence of current smokers is similar to that reported in other jurisdictions , , . This study highlights that SHS is still occurring in environments legislated to be smoke-free. By 2005, 20% of the population was still exposed to SHS in public settings, and approximately 25% of workers were still exposed to smoking at work.
It is a concern that anti-smoking legislation could shift smoking exposure from public to private places such as in vehicles as smokers have fewer locations in which they can smoke . Shifting smoking to private settings could have a significant impact on vulnerable populations. The main exposure for children occurs at home  and it has been established that SHS in homes can reach levels seen in bars . SHS in vehicles is considered to be even more hazardous because of the small-enclosed space . We found that exposures in both vehicles and at home decreased following the introduction of bans. These results are consistent with the results of a cross-sectional survey in Scotland, which found no increase in secondhand exposure among children after the implementation of a smoking ban .
Although a causal relationship cannot be proven with ecological observational data, the application of the Bradford-Hill criteria can be applied in support . First, the introduction of anti-smoking legislation was followed by declines in exposures in multiples environments across all municipalities. These results meet the consistency criterion. Second, a dose-response is seen in that municipalities with full bans had larger reported declines in SHS than partial ban locations and municipalities with no bans had the smallest declines. Third, temporality can be observed in areas in which municipalities introduced anti-smoking legislation at a later time had both higher rates of active smokers and SHS exposures and lower rates of workplace restriction. Municipalities with the earliest introduction of full smoking bans had the lowest rates of SHS exposure in a public place. Fourth, the association between anti-smoking legislation and exposure is coherent with our current understanding and the results are theoretically plausible as one would expect a decline in exposures after the implementation of a measure designed to lower exposure. We are, however, unable to meet the criteria for specificity as other variables may have influenced our results such as increased cigarette taxation.
There are some limitations to consider. Previous studies have faced methodological criticisms including the lack of individual patient-level information such as exposure to passive smoking. Ideally, a study concerned with the impact of SHS should assess individual SHS exposure. One should show that exposures to SHS have decreased following the introduction of smoking bans. To assess exposure we used two iterations of a large Canadian survey of SHS exposure in multiple environments. Using a well-validated population survey data provided us with a timely estimate of exposures over a four-year period. However, survey results were self-reported and consequently respondents may have given answers considered socially acceptable but that did not reflect actual behaviour. Questions were also limited to the population over age 12 and thus do not reflect children's smoking exposures, a population at greater physiological risk of SHS. However, it could be argued that rates of SHS exposure in vehicles and at home provide a good estimate of children's exposure. Finally, this study could only use questions from the 2003 and 2005 survey as the 2000-2001 survey contained one question about SHS exposure. This question is not directly comparable with questions in subsequent surveys. Exposure rates from all three years would have allowed relationships between smoking bans and exposures to be better delineated and trends to be determined. Between 2003 and 2005, only three municipalities (Sudbury, Durham, and Thunder Bay) had major changes to smoking regulations. These municipalities had large changes in exposure rates. For other municipalities, it is harder to determine the late effects of the introduction of anti-smoking legislation from underlying trends. Our results may overestimate the impact of anti-smoking legislation, as there has been a decreasing trend in exposure to passive smoking and the prevalence of smokers in most industrialized countries prior to the introduction of anti-smoking by-laws. Nevertheless, other research has shown a significant reduction in hospital admissions following the introduction of these laws .