"The economists (at least those who are seriously concerned with monetary policy) know that the impact of bond purchases is usually overvalued whereas many participants at the financial market who sense speculation bubbles everywhere, actually overestimate the impact of bond purchase".
Fazit - the economic blog of Frankfurter Allgemeine Zeitung: "Populäre Illusionen über Geldpolitik" (German)
Summary and video podcast of the conference "The ECB and Its Watchers XIX" on March 14, 2018 (English)