Sims的Fiscal Theory演講得到嘅一啲迴響

之前講Chris Sims在Jackson Hole有關Fiscal Theory對低通脹理解的演說重要,今次就找來一批討論這演說的文章給各位參考。

當中整理及解讀Sims演說做得較好的是Gavyn Davies在FT的文章《Sims highlights fiscal dominance at Jackson Hole》,他先簡單解釋甚麼是Fiscal Theory of Price Level:

What is the FTPL? Basically, it is a macro-economic theory that explains the behaviour of aggregate demand and inflation by joining up the balance sheets of the government and the central bank, making clear the inevitable links between them. Neither fiscal nor monetary policy can be treated as fully independent of the other…

然後再解釋Sims認為QE不能成功推高通脹,因為QE推低利率的同時,亦會減低政府的利息開支,亦即是會令政府的財赤減少,按Fiscal Theory指這是會令物價有下降壓力的。

… a reduction in interest rates will also mean a drop in debt service payments and in the overall budget deficit. Even if the increase in central bank money is permanent, Prof Sims believes that monetary policy will fail to raise inflation, unless the finance ministry “co-operates” by raising the budget deficit…

而更值得留意是按Fiscal Theory的推論,要控制通脹是需要貨幣及財政政策互相「協調」,甚至可能出現財政政策「主導」,而貨幣政策只能因應財政政策而作改變的情況,亦即學術上所謂的「Fiscal Dominance」:

…If, instead, the government insists on using the lower debt service payments to reduce the budget deficit further, it can effectively make monetary policy subordinate to fiscal policy. We are all familiar with how this can work to raise inflation if an irresponsible government (eg Brazil in the 1980s) persists in running excessive deficits that raise government debt and the monetary base. Prof Sims reminds us that this can work in reverse, with all the signs changed…

「Fiscal Dominance」在經濟政策上是一個頗負面的字眼,因為通常都是指政府不停增大開支,令財赤越大,就會迫使央行要印錢提高通脹,令政府實質負債下降,而主流的經濟分析都認為這是超級通脹的成因。


在財政政策這個課題上,Paul Krugman亦加一把口,但他是反對Sims的看法。他認為Sims指財政政策要能夠提高通脹才有能有效刺激通脹的說法,是太過強調Ricardian Equivalence這理論,並且是錯誤的。

…I think he’s saying that fiscal expansion works only if it leads to a rise in expected inflation. Or maybe not – the truth is that I’m not sure, which is one problem with too purely verbal an argument. But it’s certainly something I’ve heard from helicopter money types, who warn that something like Ricardian equivalence will undermine fiscal expansion unless it’s money-financed.

But this is a misunderstanding of Ricardian equivalence, on two levels. First, as I’ve tried repeatedly to explain, a TEMPORARY increase in government purchases of goods and services will NOT be offset by expectations of future taxes even if full Ricardian equivalence holds. The kind of argument people like Robert Lucas made sounded Ricardian, but wasn’t – it was Ricardianoid…

Brad Delong則認為Krugman的看法有錯,因為在Sims的Fiscal Theory中實際上不強調政府開支這個因素,而財政政策是透過影響實質利率這因素而改變整體需求:

…the only ways fiscal policy can affect spending and output now are if:

– deficits raise expectations of money-printing and so raise inflation π.
– deficits raise expectations of future fiscal collapse and so increase current wealth by increasing the rate at which future tax liabilities are discounted.

And as I understand Sims, quantitative easing is counterproductive: it reduces the risk premium ρ, and so raises the present value of future tax liabilities and so reduces household wealth without doing anything to alter the real interest rate…


Is this a consistent model? I am not sure. Is this the model that Chris Sims has in mind that lies behind his talk? I am not sure. Is this the right model for the questions at hand? I am pretty sure it is not one of the first five models I would write does as most relevant.