Misread signals: a misinterpretation of population-level vaping and smoking trends.

The increasing prevalence of e-cigarette use (vaping) among adolescents and young adults has ignited debate over its potential role in the initiation of cigarette smoking. Prospective cohort studies at the individual level consistently demonstrate a higher risk of smoking initiation among young people who have previously vaped when compared with those who have never vaped (sometimes called a 'gateway effect'). On the other hand, several studies analysing repeated cross-sectional data argue that vaping might decrease the risk of smoking through a 'displacement effect', as evidenced by an increasing vaping trend coinciding with a decreasing smoking trend. This perspective article examines these conflicting viewpoints in the context of a misinterpretation of these coinciding trends.