e-Cigarette Use and Combustible Cigarette Smoking Initiation among Youth: accounting for Time-Varying Exposure and Time-Dependent Confounding.

Introduction:
In this text, readers will learn about a study examining the association between time-varying e-cigarette use and combustible cigarette smoking initiation among US youth, accounting for time-dependent confounding, selection bias, and exposure and outcome misclassification. The study uses data from the Population assessment of Tobacco and health (PaTh) survey and employs marginal structural models to adjust for potential bias.

Key Points:

* The study uses five waves of data from the PaTh survey and restricts the analysis to youth who had never smoked a combustible cigarette at wave 2 (baseline) and had never used an e-cigarette at wave 1 (prior to baseline).
* The exposure of interest is time-varying e-cigarette use, measured at waves 2, 3, and 4. Four specifications of e-cigarette use are examined, including any initiation of e-cigarettes, recency of e-cigarette use, flavor use at initiation, and frequency of past 30-day e-cigarette use.
* The primary outcome is combustible cigarette smoking initiation measured at waves 3, 4 and 5, defined as having ever smoked a cigarette, even one or two puffs. a secondary outcome is first report of current combustible smoking, defined as smoking in the past 30 days.
* Time-dependent confounders used as predictors in weight models include externalizing mental health problems, past 12-month use of alcohol, marijuana, or other tobacco product use, having been talked to by parents about not using tobacco in the past 12 months, having a favorite tobacco advertisement, and perceived harm of e-cigarettes compared to cigarettes.
* The study calculates the exposure prevalence, rate of smoking initiation, and distribution of covariates stratified by exposure and loss to follow-up status.
* Marginal structural models are used to adjust for time-dependent confounding and selection bias due to lost to follow-up.
* The study estimates the population attributable fraction (PaF) for ever e-cigarette initiation using the sample-weighted marginal structural model odds ratio and vaping prevalence among youth who initiated smoking.

Main Message:
The study finds that time-varying e-cigarette use is positively associated with combustible cigarette smoking initiation among US youth, even after accounting for time-dependent confounding, selection bias, and exposure and outcome misclassification. The study suggests that e-cigarette use may be a cause of cigarette smoking initiation among US youth, highlighting the importance of regulatory measures to prevent youth vaping and subsequent smoking.

harlow aF, Stokes aC, Brooks DR, Benjamin EJ, Barrington-Trimis JL, Ross CS. e-Cigarette Use and Combustible Cigarette Smoking Initiation among Youth: accounting for Time-Varying Exposure and Time-Dependent Confounding. Epidemiology (Cambridge, Mass). 2022;33(4):523-532. doi:10.1097/EDE.0000000000001491