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dimanche 19 mai 2013

SELECTED BLOGS: PHYSICS OF FINANCE, MARCK BUCHANAN// Blind on purpose: equilibrium as a conceptual filter in economics

Courtesy of Physics of Finance  and Mark Buchanan, all rights reserved to the legals owners, Bookoflannes does not hold any right whatsoever.

Blind on purpose: equilibrium as a conceptual filter in economics

A couple of years ago, I came across this article written in The Huffington Post by economist and game theorist David Levine. It carried the provocative title "Why Economists Are Right," and argued back against all those who were then criticizing economics -- especially the rational expectations assumption -- in the aftermath of the financial crisis. Levine's article is delicately crafted and sounds superficially convincing. Indeed, it seems to make the rational expectations idea almost obvious. His argument is a masterpiece of showmanship in the manner of Milton Friedman -- its conclusion seems unavoidable, yet the logic seems somehow fishy, though in a way that is hard to pin down.

The most notable passage in this sense is the following:
In simple language what rational expectations means is "if people believe this forecast it will be true." By contrast if a theory is not one of rational expectations it means "if people believe this forecast it will not be true." Obviously such a theory has limited usefulness. Or put differently: if there is a correct theory, eventually most people will believe it, so it must necessarily be rational expectations. Any other theory has the property that people must forever disbelieve the theory regardless of overwhelming evidence -- for as soon as the theory is believed it is wrong.
Seems convincing, doesn't it? Or at least almost convincing. Is this the only claim made by the rational expectations assumption? If so, maybe it is reasonable. But there's a lot lurking in this paragraph.

When I first read this I thought -- well, he's just assuming that people will learn over time to hold rational beliefs. In other words, he simply asserts (maybe because he believes this) that the only possible outcome in our world has to be an equilibrium. If people have certain beliefs, and their actions based on these lead to a collective outcome that does not confirm those beliefs, then they'll have to adjust those beliefs. There's no equilibrium but ongoing change. From this, Levine assumes that if this goes on for a while that peoples' beliefs will adjust until they lead to actions and collective outcomes that confirm these beliefs and bring about an equilibrium. But this is simply his personal assumption, presumably because he likes game theory and has expertise in game theory and so likes to think about equilibria.

The world is much more flexible. The more general possibility is that people adjust their beliefs, act differently, and their collective behaviour leads to another outcome that against does not confirm their beliefs (at least not perfectly), so they adjust again. And there's an ongoing dance and co-evolution between beliefs and outcomes that never settles into any equilibrium.

But I've kept this essay in the back of my mind, never quite sure if my interpretation made sense, or if the hole in Levine's logic could really be this blazingly obvious. I'm now more strongly convinced that it is, in part because of a beautiful paper I came across yesterday by economist Brian Arthur. Arthur's paper is a wonderful review of the motivation behind complexity science and its application to economics. Two passages resonate in particular with Levine's argument about rational expectations:
One of the earliest insights of economics—it certainly goes back to Smith—is that aggregate patterns [in the economy] form from individual behavior, and individual behavior in turn responds to these aggregate patterns: there is a recursive loop. It is this recursive loop that connects with complexity. Complexity is not a theory but a movement in the sciences that studies how the interacting elements in a system create overall patterns, and how these overall patterns in turn cause the interacting elements to change or adapt. It might study how individual cars together act to form patterns in traffic, and how these patterns in turn cause the cars to alter their position. Complexity is about formation—the formation of structures—and how this formation affects the objects causing it.

To look at the economy, or areas within the economy, from a complexity viewpoint then would mean asking how it evolves, and this means examining in detail how individual agents’ behaviors together form some outcome and how this might in turn alter their behavior as a result. Complexity in other words asks how individual behaviors might react to the pattern they together create, and how that pattern would alter itself as a result. This is often a difficult question; we are asking how a process is created from the purposed actions of multiple agents. And so economics early in its history took a simpler approach, one more amenable to mathematical analysis. It asked not how agents’ behaviors would react to the aggregate patterns these created, but what behaviors (actions, strategies, expectations) would be upheld by—would be consistent with—the aggregate patterns these caused. It asked in other words what patterns would call for no changes in micro-behavior, and would therefore be in stasis, or equilibrium. (General equilibrium theory thus asked what prices and quantities of goods produced and consumed would be consistent with—would pose no incentives for change to—the overall pattern of prices and quantities in the economy’s markets. Classical game theory asked what strategies, moves, or allocations would be consistent with—would be the best course of action for an agent (under some criterion)—given the strategies, moves, allocations his rivals might choose. And rational expectations economics asked what expectations would be consistent with—would on average be validated by—the outcomes these expectations together created.)

This equilibrium shortcut was a natural way to examine patterns in the economy and render them open to mathematical analysis. It was an understandable—even proper—way to push economics forward. And it achieved a great deal. ...  But there has been a price for this equilibrium finesse. Economists have objected to it—to the neoclassical construction it has brought about—on the grounds that it posits an idealized, rationalized world that distorts reality, one whose underlying assumptions are often chosen for analytical convenience. I share these objections. Like many economists I admire the beauty of the neoclassical economy; but for me the construct is too pure, too brittle—too bled of reality. It lives in a Platonic world of order, stasis, knowableness, and perfection. Absent from it is the ambiguous, the messy, the real.
Here I think Arthur has perfectly described the limitation of Levine's position. Levine is happy with rational expectations because he is willing to restrict his field of interest only to those very few special cases in which peoples' expectations do correspond to collective outcomes. Anything else he thinks is uninteresting. I'm not even sure that Levine realizes he has so restricted his field of interest only to equilibrium, thereby neglecting the much larger and richer field of phenomena outside of it.

One other final comment from Arthur, with which I totally agree:
If we assume equilibrium we place a very strong filter on what we can see in the economy. Under equilibrium by definition there is no scope for improvement or further adjustment, no scope for exploration, no scope for creation, no scope for transitory phenomena, so anything in the economy that takes adjustment—adaptation, innovation, structural change, history itself—must be bypassed or dropped from theory. The result may be a beautiful structure, but it is one that lacks authenticity, aliveness, and creation.

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