Quantitative easing (QE) programs by central banks under the right conditions will always have a positive outcome for household demand, according to Willem Buiter, chief economist at Citi, who predicts that Japan and the euro zone will soon launch "massive" stimulus packages.

In a 52-page thesis released on Thursday, the economist analyses Milton Friedman's principles on "helicopter money", giving the example of permanent QE – the irreversible open market purchase of sovereign debt by central banks. He concludes that three conditions need to be met for QE to "always" boost aggregate demand.