Matt O Brien tweeted round an interesting piece by David Beckworth, which estimated a VAR to try to resolve a debate between Steve Williamson on the one hand, and Brad deLong, Paul Krugman, Noah Smith and others about whether QE was deflationary or inflationary. I responded: surely you need to identify QE shocks to recover this effect, and Matt asked 'how would you do it?'. I'm going to teach stuff like this next term, so, if I can't explain this in plain English, I have a problem.