Charles Plossner, Philadelphia Fed, om makromodeller og pengepolitiske analyse #ekstremtnerdete

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Alle gjør pengepolitkk likt og forskjellig – samtidig. Metodikken man benytter for å sette renten, beskrive verdensøkonomien, beregne adferdsmønster, sjokk osv. er i sin natur aldri komplett. Det er umulig å sette hele planeten inn i et likningssystem. Men det betyr ikke at man prøver.

En av disse tilnærmingene er DSGE-modeller. Dynamic Stochastic General Equilibrium- modeller.

Charles Possner benyttet en konferanse i mai til å snakke om disse modellene, nettopp fordi det hele tiden må stilles spørsmål ved modellene. Hvis ikke man gjør dette vil finanskriser, boligbobler etc. gjøre det.

Jeg siterer her utdrag, gå hit for hele innlegget. (Irrasjonelt plasserte tall er fotnoter, jeg tar de med.)

After spending over 30 years in academia, I have served the last six years as a policymaker trying to apply what economics has taught me. Needless to say, I picked a challenging time to undertake such an endeavor. But I have learned that, despite the advances in our understanding of economics, a number of issues remain unresolved in the context of modern macro models and their use for policy analysis. In my remarks today, I will touch on some issues facing policymakers that I believe state-of-the-art macro models would do well to confront.
[…]
More than 40 years ago, the rational expectations revolution in macroeconomics helped to shape a consensus among economists that only unanticipated shifts in monetary policy can have real effects. According to this consensus, only monetary surprises affect the real economy in the short to medium run because consumers, workers, employers, and investors cannot respond quickly enough to offset the effect of these policy actions on consumption, the labor market, and investment.1
[…]
But over the years this consensus view on the transmission mechanism of monetary policy to the real economy has evolved. The current generation of macro models, referred to as New Keynesian DSGE models,2 rely on real and nominal frictions to transmit not only unanticipated but also systematic changes in monetary policy to the economy. Unexpected monetary shocks drive movements in output, consumption, investment, hours worked, and employment in DSGE models. However, in contrast to the earlier literature, it is the relevance of systematic movements in monetary policy that makes these models of so much interest for policy analysis. Systematic policy changes are represented in these models by Taylor-type rules, in which the policy interest rate responds to changes in inflation and a measure of real activity, such as output growth. Armed with forecasts of inflation and output growth, a central bank can assess the impact that different policy rate paths may have on the economy. The ability to do this type of policy analysis helps explain the widespread use of New Keynesian DSGE models at central banks around the world.
[…]
In my view, the current rules of the game of New Keynesian DSGE models run afoul of the Lucas critique — a seminal work for my generation of macroeconomists and for each generation since.6 The Lucas critique teaches us that to do policy analysis correctly, we must understand the relationship between economic outcomes and the beliefs of economic agents about the policy regime. Equally important is the Lucas critique’s warning against using models whose structure changes with the alternative government policies under consideration.7 Policy changes are almost never once and for all. So, many economists would argue that an economic model that maps states of the world to outcomes but that does not model how policy shifts across alternative regimes would fail the Lucas critique because it would not be policy invariant.8 Instead, economists could better judge the effects of competing policy options by building models that account for the way in which policymakers switch between alternative policy regimes as economic circumstances change.9
[…]
From a policy perspective, the assumption that a central bank can always and everywhere credibly commit to its policy rule is, I believe, also questionable. While it is desirable for policymakers to do so — and in practice, I seek ways to make policy more systematic and more credible — commitment is a luxury few central bankers ever actually have, and fewer still faithfully follow.

Possner avslutter med seks punkter rundt forbedring av makromodeller:

First, I believe we should work to give the real and nominal frictions that underpin the monetary propagation mechanism of New Keynesian DSGE models deeper and more empirically supported structural foundations. There is already much work being done on this in the areas of search models applied to labor markets and studies of the behavior of prices at the firm level. Many of you at this conference have made significant contributions to this literature.

Second, on the policy dimension, the impact of the zero lower bound on central bank policy rates remains, as a central banker once said, a conundrum. The zero lower bound introduces nonlinearity into the analysis of monetary policy that macroeconomists and policymakers still do not fully understand. New Keynesian models have made some progress in solving this problem,12 but a complete understanding of the zero bound conundrum involves recasting a New Keynesian DSGE model to show how it can provide an economically meaningful story of the set of shocks, financial markets, and frictions that explain the financial crisis, the resulting recession, and the weak recovery that has followed. This might be asking a lot, but a good challenge usually produces extraordinary research.

Third, we must make progress in our analysis of credibility and commitment. The New Keynesian framework mostly assumes that policymakers are fully credible in their commitment to a specified policy rule. If that is not the case in practice, how do policymakers assess the policy advice these models deliver? Policy at the zero lower bound is a leading example of this issue. According to the New Keynesian model, zero lower bound policies rely on policymakers guiding the public’s expectations of when an initial interest rate increase will occur in the future. If the credibility of this forward guidance is questioned, evaluation of the zero lower bound policy has to account for the public’s beliefs that commitment to this policy is incomplete. I have found that policymakers like to presume that their policy actions are completely credible and then engage in decisions accordingly. Yet if that presumption is wrong, those policies will not have the desired or predicted outcomes. Is there a way to design and estimate policy responses in such a world? Can reputational models be adapted for this purpose?

Fourth, and related, macroeconomists need to consider how to integrate the institutional design of central banks into our macroeconomic models. Different designs permit different degrees of discretion for a central bank. For example, responsibility for setting monetary policy is often delegated by an elected legislature to an independent central bank. However, the mandates given to central banks differ across countries. The Fed is often said to have a dual mandate; some banks have a hierarchal mandate; and others have a single mandate. Yet economists endow their New Keynesian DSGE models with strikingly uniform Taylor-type rules, always assuming complete credibility. Policy analysis might be improved by considering the institutional design of central banks and how it relates to the ability to commit and the specification of the Taylor-type rules that go into New Keynesian models. Central banks with different levels of discretion will respond differently to the same set of shocks.

Let me offer a slightly different take on this issue. Policymakers are not Ramsey social planners. They are individuals who respond to incentives like every other actor in the economy. Those incentives are often shaped by the nature of the institutions in which they operate. Yet the models we use often ignore both the institutional environment and the rational behavior of policymakers. The models often ask policymakers to undertake actions that run counter to the incentives they face. How should economists then think about the policy advice their models offer and the outcomes they should expect? How should we think about the design of our institutions? This is not an unexplored arena, but if we are to take the policy guidance from our models seriously, we must think harder about such issues in the context of our models.

This leads to my fifth suggestion. Monetary theory has given a great deal of thought to rules and credibility in the design of monetary policy, but the recent crisis suggests that we need to think more about the design of lender-of-last-resort policy and the institutional mechanism for its execution. Whether to act as the lender of last resort is discretionary, but does it have to be so? Are there ways to make it more systematic ex ante? If so, how?

My sixth and final thought concerns moral hazard, which is addressed in only a handful of models. Moral hazard looms large when one thinks about lender-of-last-resort activities. But it is also a factor when monetary policy uses discretion to deviate from its policy rule. If the central bank has credibility that it will return to the rule once it has deviated, this may not be much of a problem. On the other hand, a central bank with less credibility, or no credibility, may run the risk of inducing excessive risk-taking. An example of this might be the so-called “Greenspan put,” in which the markets perceived that when asset prices fell, the Fed would respond by reducing interest rates. Do monetary policy actions that appear to react to the stock market induce moral hazard and excessive risk-taking? Does having lender-of-last-resort powers influence the central bank’s monetary policy decisions, especially at moments when it is not clear whether the economy is in the midst of a financial crisis? Does the combination of lender-of-last-resort responsibilities with discretionary monetary policy create moral hazard perils for a central bank, encouraging it to take riskier actions? I do not know the answer to these questions, but addressing them and the other challenges I have mentioned with New Keynesian DSGE models should prove useful for evaluating the merits of different institutional designs for central banks.

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