The effects of workplace smoke-free policies on individual smoking and quitting-related in China: evidence from repeated cross-sectional survey data

Objective Our study aims to determine the coverage of workplace Smoke-free (SF) policies in mainland China, and to assess the relationship between workplace SF policies and Second-hand smoke (SHS) exposure, smoking prevalence, smoking harm awareness, and quitting intention among smokers. Methods The Logistic regression with year fixed effects is applied to the Asia Best Workplace Mainland China study, a repeated cross-sectional dataset including approximately 14,195 employees from the 2018 survey and 14,953 employees from the 2019 survey. Results 21,275 participants (73.0%) reported working under SF policies. The overall prevalence of smoking and SHS exposure were 20.3% and 52.5%. The workplace SF policy was significantly associated with lower SHS exposure (OR: 0.501, 95% CI: 0.473-0.530), lower smoking prevalence (OR: 0.813, 95% CI: 0.761-0.869) and higher awareness of smoking harm (OR: 1.756, 95% CI: 1.612-1.913). However, workplace SF policy was not significantly associated with quitting intention (OR: 0.984, 95% CI: 0.837-1.158). Conclusion Our study identified that although most companies have established workplace SF policy ， the overall prevalence of SHS exposure remains very high. The findings supports the existence of spill-over effects of SF workplace policies. Regarding to triggering strong quitting intentions, the SF policies should consider provided in combination with available smoking cessation services. These findings provide valuable evidence to promote such policies in all workplaces.


Introduction
Because second-hand smoke (SHS) contains hundreds of chemicals known to be toxic and carcinogenic, involuntary SHS exposure contributes to premature death and causes a number of diseases in non-smokers [1][2] . The workplace is a major source of SHS exposure for adults, and the negative influence incurred by SHS exposure affects workplace productivity and contributes to absenteeism [3] .
Smoke-free (SF) policy has been a key contributor to the decline in SHS exposure. As of July 2019, 25 US states had adopted comprehensive 100% SF laws in workplaces, restaurants and bars, leading to a sharp decrease in SHS exposure from 52.5% during 1999-2000 to 25.2% during 2013-2014 [4] . Since China ratified the Framework Convention on Tobacco Control (FCTC) [5] in 2005, considerable progress has been made to reduce SHS exposure in China, particularly implementing SF policies. As a result, according to the Chinese Adult Tobacco Survey, the prevalence of SHS exposure was 63.3% in 2010 [6] , 54.3% in 2015 [7] , and 50.9% in 2018 [8] .
Despite the processes, China currently does not have a national legislation for workplace SF policy [9] , and the implementation of workplace SF policies and its impact has not been fully investigated. Most studies examining the association between workplace SF policy and SHS exposure have been conducted in western countries [10][11] . One study in 2010 reported that workplace SF policy had significant associations with lower smoking prevalence and daily cigarette consumption but not with employee quitting intentions; however, this study only collected 1070 questionnaires from one company in Shanghai [12] . Another study reported that workplace SHS exposure was associated with respiratory symptoms in Shanghai [13] . To the best of our knowledge, no more recent study has been conducted on this topic. Such knowledge is critically needed as it can help inform policymakers and health practitioners to establish stronger SF policy and conduct campaigns and interventions to reduce exposure to workplace SHS in China.
To help fill the evidence gap, we reported the findings from a repeated cross-sectional survey in the form of two years of datasets, with the goal of providing valuable evidence to promote such policies. Specifically, we aimed to (1) determine the coverage of workplace SF policies in mainland China, and (2) to assess the relationship between workplace SF policies and SHS exposure, smoking prevalence, smoking harm awareness (SHA), and quitting intention (QI) among smokers.
In addition, this paper extends prior research along two dimensions. First, it extends to participants living in the entire mainland of China, rather than a city or province. Although our sample is not nationally representative, we believe it can provide more valuable information than can a local sample. Second, we use repeated cross-sectional data taken in 2018 and 2019, rather than a single dataset. By using survey data in different years, this paper considers the possible systematic differences between years: using fixed effects to control for year-specific characteristics.

Study design and participants
The Asia Best Workplace Mainland China (ABWMC) programme was a repeated cross-sectional survey that aimed to support companies in building healthy workplaces through policy, infrastructure, and culture. The

SHS exposure and workplace SF policies
The presence of SHS exposure was measured using the question 'How many days per week do you usually suffer from SHS exposure at the workplace for more than 15 minutes a day? A: almost every day; B: 4-6 days; C: 1-3 days; D: never'. Respondents who answered D were considered to be working without SHS exposure. The presence of a workplace SF policy was measured using the question 'Does your company have SF policies? A: no SF policies; B: SF policies that permit smoking in parts of the indoor area; C: SF policies that completely ban smoking inside the building; D: I have no idea'. Respondents who answered C were considered as working under an SF policy.

Smoking and quitting intentions
Smoking was measured by the following question: 'Do you smoke now? A: yes, every day, B: yes, only occasionally, C: I have quit smoking, D: never'. Respondents who answered A or B were considered to be current smokers. Quitting intentions were measured using the question 'Are you going to quit smoking? A: yes, within a month, B: yes, within 6 months, C: yes, but not within 6 months, D: no plan for quitting'.
Respondents who answered A or B or C were considered as intending to quit.

Smoking harm awareness
Smoking harm awareness was measured by the following question 'To the best of your knowledge, which diseases can be caused by smoking? A: stroke, B: heart disease, C: lung cancer, D: cardiovascular disease, E: chronic obstructive pulmonary disease, F: asthma, G: I don't know.' Respondents who chose all the answers from A to F were considered to have smoking harm awareness.

Other control variables
In addition to these key variables, other variables such as sex, age, marital status, ethnicity, education, chronic diseases, job position, and night-shift duty were collected as control variables.

Data analysis
Logistic regression was used to estimate the effects of workplace SF policies on individual smoking and quitting behaviours. The specification of our empirical model was as follows: SHS exposure (or smoking)=β0+ β1 SF policy+ γXi + + .
The dependent variable was either SHS exposure or smoking. The explanatory variable SF policy was a dummy indicating whether an employee was working for a company that had an SF workplace policy or not is a variety of other control variables, is the year fixed effects to control for year-specific factors, and is the error term. We also perform regression with each year's sample separately.
To determine whether such policy had effects on smoking harm awareness and quitting intention, we changed the dependent variable and ran the following regression: SHA (or QI)=β0+ β1 SF policy+ γXi + + .
Our analyses used all participants for whom the variables of interest were available, with no imputation for missing data. All statistical analyses were performed using SPSS 19.0.

Role of the funding source
The funders of the study had no role in the design of the study; collection, analysis, or interpretation of the data; or the writing of the paper.

Discussion
To the best of our knowledge, our study was one of the largest surveys to date to evaluate the impacts of workplace SF policies on SHS exposure and smoking-related behaviour in a Chinese population. The results showed the following: (1) most companies had established workplace SF policies; however, the overall prevalence of SHS exposure remains very high (52.5%); (2) workplace SF policies showed a strong association with lower SHS exposure, lower smoking prevalence and higher harm awareness of smoking; and (3) the association with smokers' quitting intentions was weak.
Article 8 of the WHO FCTC requires parties to adopt and implement measures to reduce exposure to tobacco smoke in indoor workplaces, indoor public places, public transport and other public places [5] . Since the FCTC was ratified in 2005, the Chinese government has made a serious commitment to reduce or eliminate SHS exposure in workplaces; the prevalence of SHS exposure was reduced from 63.3% in 2010 [6] to 50.9% in 2018 [8] , which was similar to the 54.7% found in our study. Moreover, our study found a strong correlation between workplace SF policies and lower SHS exposure, which was consistent with a systematic review suggesting that SHS exposure in the workplace decreased significantly from 20% to 8% after an SF policy was implemented [14] .
As an impressive finding, our data suggested that the influence of workplace SF policies was not limited to a reduction in SHS exposure. Therefore, reducing SHS exposure is not simply the result of the implementation of workplace SF policies. Rather, the change may reflect a synergism of multiple factors, with such forces working in conjunction to contribute to lowering SHS exposure. Our findings reinforce the recommendations of a previous study that SF policies may lead to spreading of smoke-free norms in the workplace [15] . Furthermore, our study actually supports the existence of spill-over effects of SF workplace policies. How do these factors interact with one another? Is there any potential mediator? All these questions merit further research. A detail description of the internal mechanisms and possible pathways will be reported elsewhere [16] .
In general, workplace SF policies should motivate smokers to quit by making it more difficult to smoke; for example, smokers must go out of their workplace to smoke and increase the time cost of smoking [17] .
However, consistent with the findings of a previous study [11] , no significant association was found between workplace SF policies and more positive quitting intention. One possible explanation was the 'hardcore' smokers who may be less motivated to quit regardless of SF policies at worksites; therefore, more intensive intervention should be provided for them [18] . Another explanation was the violation of workplace SF policy.
The effects of workplace SF policy would be undermined when it is violated by large numbers of smokers who continue to smoke, and this non-compliance may jeopardise a smoker's quitting intention because they are surrounded by others who continue to smoke [19] .
Our study has several limitations. First, the ABWMC programme was launched in 2018, and we only had two years of repeated cross-sectional data for this estimation. As a result, we cannot infer a causal relationship, which is an inherent characteristic of all cross-sectional studies. Second, workplace SF policy was self-reported without verification, and respondents' definitions of workplace SF policy may vary. Third, the companies who joined the ABWMC programme were mainly located in developed areas of China; therefore, our data are not a nationally representative sample. Fourth, we only measured SHS exposure in the workplace, and SHS exposure from elsewhere was neglected. In addition, we did not measure smoking reduction or the duration of workplace SF policies and policy enforcement, including incentives and penalties.
Despite these limitations, our findings have practical policy implications. The results of the present study could encourage policymakers and health practitioners to accelerate the implementation of SF policy and thereby contribute to a broader SF culture in the workplace. In particular, because the effect of current workplace SF policy on quitting intention was weak, the SF policies should be provided in combination with smoking cessation services. As with the results of the ABWMC programme, our findings will be disseminated to the participating companies, which may not only encourage those struggling to catch up but will also encourage them to establish more comprehensive workplace SF policies and further improve health status in China.

Conclusion
Using ABWMC programme data, this study provides a comprehensive picture of the impact of SF workplace policies on possible smoking-related behaviour using Chinese data. It identified that although most companies have established workplace SF policy，the overall prevalence of SHS exposure remains very high. The findings supports the existence of spill-over effects of SF workplace policies. Regarding to triggering strong quitting intentions, the SF policies should consider provided in combination with available smoking cessation services. These findings provide valuable evidence to promote such policies in all workplaces.

Framework Convention on Tobacco Control (FCTC)
Smoking harm awareness (SHA), and quitting intention (QI) Asia Best Workplace Mainland China(ABWMC)

Ethics approval and consent to participate
This study was approved by the Peking University (Ethical approval number: IRB00001052-18055).
Informed consent obtained from online.

Consent for publication
Not applicable

Availability of data and material
The data of the studies is accessible via Peking University, School of Public Health.