The effectiveness of central banks’ asset purchase programmes (‘quantitative easing’) has been a subject of intense debate in both academic and policy circles. Much of the analysis is conducted by the staff of central banks themselves, which is not unlike pharmaceutical firms evaluating their own drugs. Indeed, as this column shows, papers by central bank researchers in the US, the UK, and the euro area report systematically larger effects of unconventional monetary policy on output and inflation than papers by independent academics. This is not to argue that central bank research should be discounted or to question its credibility – but it does highlight a previously unexplored conflict of interest.