Public support for smoke-free policies in outdoor areas and (semi-) private places: a systematic review and meta-analysis 91 4 Discussion This systematic review and meta-analysis including data from almost 900,000 unique participants from 33 different countries indicates high levels of support for smoke-free policies in the majority of outdoor areas and (semi-)private places. Support was particularly high for smoke-free places where children are commonly exposed to tobacco smoke, such as cars carrying children, playgrounds, and school grounds. Except for outdoor private areas, support was 50% or higher for all places evaluated. Non-smokers and ex-smokers were more in favour of smoke-free policies than smokers. Strengths of the study include the comprehensive search in eight databases, and the absence of any language restriction. With 107 reports included covering data from 33 different countries, the body of existing literature describing support was substantial. Data from 99 studies were pooled for 15 different areas of smoke-free policies, and we accounted for potential clustering at country-level by applying a three-level meta-analysis. Hence, we accounted for variance at participant, study, and country level. In addition to the meta-analysis we conducted subgroup analyses, meta-regression, and sensitivity analyses, providing additional insight in the patterning of public support for novel smoke-free policies. Sensitivity analyses generally showed no meaningful differences in support between lower and higher risk-of-bias studies, suggesting that the evidence is robust. A limitation of this study is that generalisability to other countries may be limited. Although there was no indication for publication bias, countries included might be subject to bias, as it is likely that countries planning for novel ways to reduce negative harms of tobacco among the population are more likely to survey support for such policies. This is reflected by the large number of studies from the USA where traditional smoke-free policies are already commonplace, and the low proportion of studies from LMICs, where governmental actions regarding tobacco are commonly more limited. Thirteen reports with 69 estimates in our systematic review were from 11 LMICs. The majority of estimates included in the metaanalysis (33%) however, were from one country (i.e. republic of Georgia). Other limitations of this study concern the different ways support was assessed. We did take into consideration the type of answer categories, and did not find large differences when participants were asked if they supported smoke-free policies with a yes-no question or on a Likert scale. Some papers reported proportion not in favour of a policy and outcome estimates were reversed. Although for one
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