While data on Thursday showed euro zone inflation fell to a four-year low of 0.7 percent on year in October, it may not offer much support for the view QE is damping inflation.
"They have a lot of the key economies going through austerity measures, so the lower inflation outcome may not be solely due to a lot of QE," noted Alvin Liew, senior economist at UOB in Singapore.
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Since peripheral European economies using the euro can't allow their currency to depreciate to match weak economic conditions, domestic prices there must fall to match low growth expectations, noted Leif Eskesen, an economist at HSBC.
It's also not clear the assets purchases are "unproductive."
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Central banks are also targeting mortgages, noted Eskesen. "It's helping to keep interest rates low. It's helping to keep the yield curve flat," he said. "It encourages, to some extent, more lending and risk taking," helping to support the demand side, he said, adding QE may have helped avert deflation.
"I severely doubt inflation expectations would have been higher in the absence of QE," added Robert Prior-Wandesforde, an economist at Credit Suisse. But he noted a better question would be whether QE is having any real impact on economic activity. "It's not at all clear it's boosting investment at all, let alone unproductive investment," Prior-Wandesforde said. He noted banks are lending cautiously, making the chances of lending to unproductive enterprises consequently smaller.
But he added, the QE-driven liquidity is pumping up asset prices that could suffer when the liquidity is withdrawn. "Bubble turning to bust has a reasonable probability and the bust could ultimately lead to deflation, but that's a second- or third-round effect and one that is unlikely," he said.
— By CNBC's Leslie Shaffer. Follow her on Twitter: @LeslieShaffer1