O princípio básico da política monetária é simples: juros baixos estimulam a actividade económica e impulsionam os preços; juros altos retraem a procura e pressionam a inflação para baixo. Aliás, o princípio é tão simples que qualquer pessoa pode fazer de Janet Yellen (ou Mario Draghi) em simuladores deste género.
Mas e se as coisas forem mais complicadas do que isto? Parece estranho, mas há quem sugira que juros baixos podem, no longo prazo, acabar por conduzir à deflação. No centro do debate está a) a equação de Fisher, segundo a qual a taxa de juro nominal é igual à taxa de juros real mais a inflação; e b) a ideia de que o banco central só pode afectar a taxa de juro real no curto prazo. Juntando ambas as peças, chega-se à conclusão de que uma taxa directora de 0% acabará, pouco a pouco, por ’empurrar’ para baixo a inflação, de modo a que a equação de mantenha válida.
Na verdade, é um pouco mais complicado do que isto. Mas o debate entre estes neo-fisherites (intraduzível) e o resto da classe está aí: Monetary policy with interest on reserves (John Cochrane), A dirty little secret (David Andolfatto), Reality might topple a beloved theory (Noah Smith), On neo fisherianism and adaptative learning (Tony Yates). E um post mais antigo, que faz uma boa súmula do debate em meados de 2014: The Neo-fisherite rebellion (Noah Smith). O trecho de baixo é de Tony Yates.
1 I wonder if the debate isn’t gettting too hung up on models using rational expectations. RE is just a convenient tool, probably a not very realistic one. If we drop RE and use a version of the New Keynesian model with adaptive learning instead, we would arrive at answers that sound pretty much like what central banks already say. And nothing like neo-Fisherianism. Note ‘rational expectations’ refers to when agents in the model have forecasting rules for inflation that are the same as the rules you would have if you knew exactly how the model worked. ‘Adaptive learning’ means here: behaving like an econometrician, basing forecasts of the future on how inflation (and other things) have depended on past values of things you can see, and updating your forecasting rules as new data comes in, either validating or flouting the rule you used last time.
2 Relative to historically followed policy rules, a policy that cut rates to the zero bound and held them there, in the absence of any other shocks hitting the economy, would cause explosive upward movements in inflation. The explosions would come from the initial upward movements in inflation causing private agents’ extrapolative forecasting rules to change, which would amplify the past movement, causing more forecast rule revisions, and so on.
3 The coincidence/comovment of falling interest rates and inflation could only come from policy responding to an inflation-depressing shock, and incompletely stabilising it.
4 If the Fed had shifted its preferences privately to deliver very low inflation, that would eventually deliver low interest rates and low inflation. But, initially, it would have required an interest rate increase. This seems a pretty implausible account of what happened recently. For starters, interest rates did not increase since the onset of the crisis. Second, FOMC members did not lower their inflation targets, or, at least if they did, they did it privately [and it didn’t even make the transcripts released] and contradicting what they had told us about their long term view of inflation.
5 In this model, although the Fisher equation will prevail in the long run, one can’t deliver a particular level of inflation with an interest rate peg worked out from this equation, unless one starts from steady state and there are no shocks. In an economy buffeted with shocks, a fixed interest rate will cause explosive movements in inflation one way or the other, depending on the luck of the draw.
Bringing this together. If you believe in a more realistic version of the popular New Keynesian model modified so that we have inflation expectations formed by adaptive learning, rather than rational expectations, then you can’t believe that low infaltion was caused by lowering nominal interest rates. You’d believe things that sound pretty much like the received wisdom, the words coming out of the mouths of central bankers.