These observations confirm that the relationship between economic activity and inflation, as postulated by the Phillips curve, has continued to play a role at the euro area level.3 The link between inflation and economic slack is complicated by several factors. On the one hand, the degree to which prices respond to slack may depend on the state of the business cycle and could change, in particular, in severe and protracted recessions. The empirical evidence on such non-linearities, however, is not conclusive. On the other hand, secular shifts in the economy may have altered the relationship between inflation and economic slack. For instance, the trend towards a deeper integration of the global economy over the last decades is likely to have increased the importance of global relative to local conditions in shaping domestic cost and price pressures. A further often-cited factor is demographics – and especially the trend towards greater longevity – which may have interacted with cyclical conditions by inducing households to save more and, ultimately, put downward pressure on inflation.4 Empirical evidence on this issue is inconclusive and demographics would 2/5  BIS central bankers' speeches  only have lasting effects on the economy if left unattended by monetary policy. Overall, these observations have three important implications for monetary policy. First, the evidence confirms that the core Phillips curve connection linking inflation formation to resource utilisation remains a key ingredient in explaining the prevailing disinflationary pressures.
In the summer of 2014, the persistence of disinflationary forces could be clearly identified: first, measures of underlying inflation had been drifting down in synch with headline inflation for more than a year, and had reached historical lows.7 Second, for the first time since the inception of Monetary Union, longerterm inflation expectations had started to fall as well. Such fundamental risks to price stability required a forceful monetary policy response. Accordingly, the ECB deployed a series of unconventional monetary policy measures to ensure price stability. The comprehensive package of June 2014 comprised targeted long-term refinancing operations (TLTROs) and a cut of the deposit facility rate, moving it into negative territory. This package was combined with a, to start with, small asset purchase programme initially involving only private sector securities, which was later expanded to include public sector securities (becoming known as the public sector purchase programme – PSPP) and then scaled up over time. These measures were accompanied by further cuts in the deposit facility rate and further TLTROs; moreover, they have been complemented by our forward guidance.