1/14 How do e-cigarettes (ECs) affect cigarette smoking among youth? My new paper with @FloeFoxon simulates each scenario and finds out which one best matches actual trends... https://t.co/dBB7kcnTls @jgitchell @mikepesko @SwitchFinder @jkelovuori @TobPolicy @Clive_Bates

2/14 First, let's talk about why this question is so difficult to answer: COUNTERFACTUALS. We can't know the alternate-reality answers, like which smokers would have never started in a world without ECs, and which nonsmokers would now be smoking without ECs as an option.

3/14 So, the best we can do is use fancy/sophisticated methodologies to estimate what would have happened to youth smoking rates in the absence of ECs. In our case, simulation modeling

4/14 First, we look at the declining smoking trends *that were already happening* before ECs came (~2010), and project them into the present. This is our BASE-CASE SCENARIO about what smoking trends would be if ECs were never invented. Actual trends were LOWER than this base-case

5/14 Side note about terminology: We use the term “catalyst” instead of “gateway,” because “catalyst” is more precise about the claim we are modeling (that ECs are used first, and then causally lead to smoking). Whereas "gateway" can include other mechanisms like renormalization.