[apathy]

they seem to be fixated on how shiny and new L1 penalties are, in 2014. Greg Ridgway started using gradient boosting machines (GBM) for propensity scoring in the early 2000s, and I didn't see them cite him, so I kind of hate them already. On the other hand, at least GBM works well.

I'm no economist, though. Perhaps this is novel at NBER. It's just odd to see someone acting like using an ensemble to enable data-driven model selection is something new.

nb. I didn't read the entire 76-page paper (partly because it's obscenely verbose). A quick skim and here are my from-the-hip remarks. If they suck, I'll refund every cent you paid me ;-)