The authors admit this in the paper. They write: "This is a cross-sectional study, which only allows us to identify associations, not causal relationships."

The study is notable because it found that even among dual users, there was a substantial improvement in respiratory health symptoms and a significant increase in several measures of acute lung function, especially small airways flow rates. Thus, the results of this study suggest that dual use of cigarettes and electronic cigarettes might result in respiratory health improvement if the reduction in cigarette use is dramatic, as it was among the dual users in this study.

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