Gateway effects and electronic cigarettes

Background E‐cigarettes are alleged to be a gateway to cigarette smoking in non‐smokers. This study examines whether the gateway theory has value, whether the criteria to establish causality have been met and what type of evidence is required to test this theory. Analysis Experiments are impractical, and we may not be able to test properly the gateway effects via observational studies that simply adjust for confounders. Multivariate models...