This is a fair point, although it should be noted that 19 states legalized gay marriage in 2014 compared with only 16 states in any of the prior years examined.

This is a fair point, although it should be noted that 19 states legalized gay marriage in 2014 compared with only 16 states in any of the prior years examined. And 8 of those 16 were in 2013. So, 27 out of 35 states examined legalized same-sex marriage either in 2014 or within one year prior. I would be interested to learn just how much the data from those other 8 states affect the weighted average the authors used to identify the association. By the way, if you look at the accompanying figure 2 and figure 3 in the JAMA article, you will see just how noisy the data is for both Wave 1 and Wave 2 states, as well as the relative lack of post-2014 data points. Honestly, just looking at those two charts should be enough to give you a healthy skepticism about the conclusion, whatever your ideological views.