BACKGROUND AND AIMS Exploring the relationship between vaping and smoking in young people is a key area of research that can inform e-cigarette policy. Rigorous evidence mapping and synthesis have highlighted gaps and methodological concerns in the evidence base. This study provides recommendations for the conduct and reporting of future quantitative primary research exploring e-cigarette use and later cigarette smoking in young people (≤29 years).

METHODS We developed a draft version of recommendations based on the critical appraisal of studies, findings of a systematic review and an evidence and gap map. We used an anonymized on-line survey to run a consultation exercise with stakeholders, including researchers, non-profit/charity workers and clinicians. Respondents rated the perceived importance of each draft recommendation on a 5-point Likert scale and provided open-ended comments, where relevant. We developed a final set of recommendations based on this stakeholder input.

RESULTS We initially came up with a list of 22 recommendations, which 36 stakeholders rated in the on-line survey. Most were researchers (n = 26) and from the USA (n = 18). Following feedback, this resulted in a final set of 23 recommendations, including recommendations for planning, data collection, data analysis and reporting. Examining causes of differences in vaping-smoking associations, including equity factors (e.g. socioeconomic status) and contextual factors (e.g. jurisdiction levels), and generating representative longitudinal data from countries other than the USA, Canada and UK, particularly low- and middle-income countries, were strongly endorsed recommendations. A new recommendation to report characteristics of e-cigarettes (e.g. flavours) was added.

CONCLUSIONS This study provides 23 recommendations for conducting and reporting future quantitative research exploring e-cigarette use/availability and later combustible cigarette smoking in young people. Most of the recommendations are specific to studies using repeat cross-sectional data tracking population trends and to longitudinal cohort studies tracking behaviours in individuals.