Stanton CA, et al. - In this analysis, researchers investigated the bidirectional patterns of ENDS (e-cigarettes) and cigarette use among US youth over one year and the link between frequency of ENDS use with changes in cigarette smoking using propensity score matching. They identified 11,996 participants who had two waves of available data (W1 2013-2014; W2 2014-2015) drawn from the longitudinal Population Assessment of Tobacco and Health (PATH) Study. Assessing the effect of W1 ENDS use on W2 cigarette smoking, they identified that W1 cigarette-naïve ENDS use was correlated with W2 ever cigarette smoking. W1 ever ENDS use did not affect change in cigarette frequency at W2, and 1-5 days ENDS use vs ever, no past-30-day ENDS use was correlated with a statistically significant decrease of W2 smoking days. W1 6+ day ENDS users did not show a decrease in frequency of cigarette smoking. Results thereby emphasize the significance of targeting both cigarettes and ENDS in early tobacco prevention efforts with youth.