Fourth, the absence of baseline data before the intervention did not allow for a before-and-after comparison and analysis. Respondents shown the TV ad before were not asked the questions about their knowledge of the effects of smoking and passive smoking. Fifth, considering the nature of the delivery of MMCs, the inclusion of individual randomization was not possible in this study, and the possibility that the consequences were biased by unequally distributed antecedent factors affecting outcome cannot be entirely discounted. Sixth, the data were analyzed from one secondhand smoking advertisement launched in one city in western China, and this limitation may affect the study generalizability in other areas. China is the world’s most populous country with 1.3