1. ASH Factsheet: Use of E-Cigarettes (Vapourisers) among Adults in Great Britainhttp://ash.org.uk/information-and-resources/fact-sheets/use-of-e-cigarettes-among-adults-in-great-britain-2017/
2. Current Cigarette Smoking Among Adults — United States, 2005–2014
3. Special Eurobarometer 458: Attitudes of Europeans towards Tobacco and Electronic Cigaretteshttp://ec.europa.eu/commfrontoffice/publicopinion/index.cfm/Survey/getSurveyDetail/search/458/surveyKy/2146
4. Trends in Electronic Cigarette Use in Englandhttp://www.smokinginengland.info/latest-statistics/
5. Rookgedrag in België 2017https://www.kanker.be/sites/default/files/stichting_tegen_kanker_-_enquete_rookgedrag_2017_1.pdf