It seems like it might not just be a replacement effect, though. Adding those numbers together, and pretending that 2016 == 2017, you get an increase from 17.3%

It seems like it might not just be a replacement effect, though. Adding those numbers together, and pretending that 2016 == 2017, you get an increase from 17.3% of kids using either in 2011, to 19.3% in 2016/2017. Perhaps you can make an argument that, lacking tar and being (purportedly?) less addictive, e-cigs are enough less bad that a net increase in the number of kids consuming nicotine is an acceptable price for halving the number of kids who are smoking cigarettes. That's a more arguable argument, though.