From our standpoint, neither of these explanations hold much water.
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Fortunately for fans of logic, there is a third explanation that is much more plausible, and has the benefit of having data behind it. Despite my extreme criticism of Fed actions in recent years, I would argue that QE2 has in fact been "successful" over the short-term, but not through any monetary mechanism. Rather, QE2 has been successful a) by creating a burst of enthusiasm that released some pent-up demand in the same way that Cash for Clunkers and the new homebuyer tax credit did, and b) by encouraging investors to believe that the Fed has provided a "backstop" for stocks and other risky assets, creating a speculative blowoff in these securities, to the detriment of what investors perceive as "safe" assets, which ironically includes Treasury securities.
...
Fortunately for fans of logic, there is a third explanation that is much more plausible, and has the benefit of having data behind it. Despite my extreme criticism of Fed actions in recent years, I would argue that QE2 has in fact been "successful" over the short-term, but not through any monetary mechanism. Rather, QE2 has been successful a) by creating a burst of enthusiasm that released some pent-up demand in the same way that Cash for Clunkers and the new homebuyer tax credit did, and b) by encouraging investors to believe that the Fed has provided a "backstop" for stocks and other risky assets, creating a speculative blowoff in these securities, to the detriment of what investors perceive as "safe" assets, which ironically includes Treasury securities.