This Yale piece is quite good. My recent
AB32 webinar convinced me that there is great interest in the Cap & Trade field experiment that California is now launching. The challenging issue for research nerds is that there is no control group and there will be general equilibrium effects! In such a setting, how do we evaluate whether the experiment is a success or not? What "double difference" do you plan to do to estimate the "average treatment effect"? Nerds of the world, unite! and start to think about these hard questions.