Christopher J. Neely, How Persistent are Monetary Policy Effects at the Zero Lower Bound?, Working Papers 2014-4, Federal Reserve Bank of St. Louis, 09 Feb 2014.

“Event studies show that Fed unconventional announcements of forward guidance and large scale asset purchases had large and desired effects on asset prices but do not tell us how long such effects last. Wright (2012) used a structural vector autoregression (SVAR) to argue that unconventional policies have very transient effects on asset prices, with half-lives of 3 months. This would suggest that unconventional policies can have only marginal effects on macroeconomic variables. The present paper shows, however, that the SVAR is unstable, forecasts very poorly and therefore delivers spurious inference about the duration of the unconventional monetary shocks. In addition, implied in-sample return predictability from the SVAR greatly exceeds that which is consistent with rational asset pricing and reasonable risk aversion. Restricted models that respect plausible predictability in asset returns are more stable and imply that the unconventional monetary policy shocks were fairly persistent but that our uncertainty about their effects increases with forecast horizon. Estimates of the dynamic effects of shocks should respect the limited predictability in asset prices.”