Finally, these general considerations aside, it is worth questioning whether such arguments about monetary policy spillovers actually hold for the euro area. For example, if we look at spillovers into asset prices, there is no evidence that the announcement of the APP induced a surge in portfolio flows into emerging market economies.
At the same time, other policies such as fiscal and, more importantly, structural have a significant role. We should not, after all, forget the classic lesson of Jan Tinbergen that there need to be just as many instruments as there are targets.