Mark Thoma je danes objavil odlično razmišljanje o optimalnosti makro modelov. Njegov sklep: Nobeden. Ali bolje rečeno, nobeden ni primeren za vse situacije. In (tudi) od tod takšne težave ekonomije glede sposobnosti napovedovanja makroekonomske dinamike.

Medtem ko je neo-keynesianski model (DSGE) relativno dobro deloval v času Velike moderacije (1984-2007), pa je povsem odpovedal v času sedanje Velike recesije. Na drugi strani je standardni IS-LM model izjemno prikladen za tovrstne situacije, ko imamo opravka z veliko negotovostjo glede agregatnega povpraševanja, ničelnimi obrestnimi merami in likvidnostjo pastjo, ni pa primeren za obdobja zmernih gospodarskih gibanj.

I don’t think anyone disagrees that one grand model attempting to capture every feature in the economy would be too complicated and unwieldy to be of use, and that models need to be adjusted depending upon the questions we are interested in. The debate is about which class of models we should use as the foundation for the various extensions needed to answer specific questions.

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Where I disagree with many of my colleagues is in the assertion that we should limit ourselves to a single class of models, e.g. variations on the New Keynesian model. Going back to the map example, is one class of maps – globes – the best type of map for all purposes? Of course not, and I don’t think economic models are any different. There is no single class of macroeconomic models that is best for all questions, at least not yet.

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The New Keynesian model was built to explain a world of moderate fluctuations in GDP. It features temporary price rigidities, and the macroeconomic aggregates in the model are consistent with the optimizing behavior of individual consumers and producers. For certain types of questions – how should policymakers behave to stabilize an economy with mild fluctuations induced by price rigidities – it is the best model to use. […] When a different world emerged, a large financial shock and the ensuing Great Recession, the model was of little use in guiding policymakers or explaining what had happened.

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The IS-LM model, on the other hand, was built in the aftermath of the Great Depression to examine precisely the kinds of questions we faced throughout the Great Recession, issues such as a liquidity trap, the paradox of thrift, and how policymakers should react in such an environment. Why is it surprising that a model built to explain a particular set of questions does better than a model built to explain other things?

Vir: Mark Thoma, The Fiscal Times