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Markets are Efficient if and Only if P = NP

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21–30 of 86 posts

Re: Markets are Efficient if and Only if P = NP

#21
post #10

"The majority of financial academics believe in market efficiency and the majority of computer scientists believe that P ≠ NP. The result of this paper is that they cannot both be right: either P = NP and the markets are efficient, or P ≠ NP and the markets are not efficient." I'll hazard a guess the computer scientists are right, but most financial academics will probably get by just fine if markets are approximatel…

I'm pretty sure financial academics don't claim that markets are efficient, but that they tend towards efficiency.

For those wanting to know more about the efficient-markets hypothesis, Wikipedia has a good article: http://en.wikipedia.org/wiki/Efficient_markets

My amateur understanding is that most academics get that it's a simplifying assumption, but that a lot of other people treat it as a guarantee. It's sort of like people who learn a little about evolution and then conclude that a) we are the most highly evolved organism on the planet, and b) we are therefore perfect.

Re: Markets are Efficient if and Only if P = NP

#22
post #16

Earlier quoted context omitted.

I'm not sure you understand what the free market is, or how it works. The fall of 2008 wasn't a free market. In particular, the government was forcing lenders to accept more risk (viz sub-prime borrowers) than they would otherwise have done. Also, the lenders themselves incorrectly modeled their risk exposures. None of your objections: what about information asymmetry? What about borked incentives? What about just pl…

So, no true scotsman? We're in the real world here. If the real world held up to a given person's theory, communism would've worked. You just have a different theory. I'm not claiming markets are terrible, they're usually the best way to do things. But when you pigeonhole yourself into an absolutist position, you've guaranteed that you're going to be flagrantly wrong sometimes.

when you pigeonhole yourself into an absolutist position

That's a fair criticism of my reply. My initial statement almost had a flavor of "free markets are perfect", whereas what I really believe is that "free markets are the best system possible".

So, no true scotsman?

But I don't think that's a fair criticism. There is a clear, well-defined concept of "free market"; it's not like I keep backing off my statement every time someone scores a hit on my argument. If the theory can explain exactly why the various regulations on the market have the observed result -- that is, if it has scientific predictive value as opposed to an irrational belief system -- then I don't think I'm susceptible to this criticism.

In high school physics we did Newtonian mechanics assuming a frictionless surface, etc. It turns out that our experimental results didn't match up with what really happened, because we had friction and other factors. But we learned more physics, so even though we didn't have access to that frictionless surface, we could explain why the results differed, and predict just how those differences would appear (friction is proportional to downward force, etc.).

You're criticizing the market theory because the observed results have those "frictional" differences, even though we can tell you what is causing the friction, and predict (albeit to a limited degree at this point) what the future effects of proposed "friction" (i.e., regulation) would be.

Re: Markets are Efficient if and Only if P = NP

#23
post #8

Earlier quoted context omitted.

Was the fall of 2008 "extremely close" to optimal? I'd submit that worldviews based on 1-dimensional criteria like "market!" or "hayek!" fall pretty far short of the mark. Although I can see the attraction. It's nice to simplify things to a level where a human being can actually have the answers with a high degree of confidence. Both the tea-party-hayekians and the linked paper fall into this trap.. what about inform…

I'm not sure you understand what the free market is, or how it works. The fall of 2008 wasn't a free market. In particular, the government was forcing lenders to accept more risk (viz sub-prime borrowers) than they would otherwise have done. Also, the lenders themselves incorrectly modeled their risk exposures. None of your objections: what about information asymmetry? What about borked incentives? What about just pl…

Bad incentives: it's the incentives (see "Invisible Hand") that make things work properly! To the extent that the incentives are wrong, these are the regulations, the aberrations that make things deviate from the free market.

It's fairly common for traders managing (or depending how you look at it, gambling) other people's money to be paid a percentage of the total money under management (for the sake of argument, let's say 0.5%) plus a much larger percentage (10%) of the upside.

That this leads to perverse incentives is, I hope, obvious to everyone here - I've literally sat down with traders and run best guess numbers incorporating the risk of getting fired (or losing investors, shutting down the fund, etc.), difficulty finding another gig doing the same thing vs. the potential gains, and the mathematical conclusion is almost always the same: go all-in, take on as much risk as you can possibly manage, and you'll do better personally than if you invested safely. The only real question is a moral one, i.e. do you care enough about doing what's right to actually try to preserve your client's money rather than gamble it away for a shot at a bigger prize? [Interestingly enough, I've found that most do, the problem is that there's a small subset that don't give a shit, and their abuses taint the entire field]

This type of risk-seeking unquestionably played a role in the recent collapse, I don't really see how that can be denied - sure, government incentives triggered the initial housing market buildup and drop, but IIRC that was initially only a 4% correction, it was only because of how massively leveraged the financial sector had become w.r.t. credit that such a drop had any impact on anything at all.

Do you really think the payment incentives in the financial sector are helping the market work properly? Or do you think that those payment schemes (a nibble of the principal and a chomp of the upside) are somehow caused by government meddling?

IMO, the problem is that it's a mistake to assume that the negative effects of "government meddling" end with official government. Any time you put a group of people together and have them agree on rules and regulations, especially ones about how to distribute money amongst themselves, you run the risk of creating incentives where individually self-interested actions actually work against the group. This applies to corporations, clubs, families, teams, etc., just as much as it does to governments.

Re: Markets are Efficient if and Only if P = NP

#24
post #4

Title should read: "If markets are perfectly efficient P=NP" rather than "Markets are efficient if and only if P = NP". For example, say P = NP, but the only person that knows the proof is me. If I start using my knowledge that P = NP to trade I will not have enough capital to swing the market to truly reflect the efficient price. Therefore it does not follow that if P = NP the market will be perfectly efficient, whi…

Or maybe just "Markets can be perfectly efficient if and only if P = NP".

Re: Markets are Efficient if and Only if P = NP

#25
post #16

Earlier quoted context omitted.

So, no true scotsman? We're in the real world here. If the real world held up to a given person's theory, communism would've worked. You just have a different theory. I'm not claiming markets are terrible, they're usually the best way to do things. But when you pigeonhole yourself into an absolutist position, you've guaranteed that you're going to be flagrantly wrong sometimes.

when you pigeonhole yourself into an absolutist position That's a fair criticism of my reply. My initial statement almost had a flavor of "free markets are perfect", whereas what I really believe is that "free markets are the best system possible". So, no true scotsman? But I don't think that's a fair criticism. There is a clear, well-defined concept of "free market"; it's not like I keep backing off my statement eve…

I'm criticizing fundamentalist market theory, and the practice of turning your brain off.

The crash of 2008 was preceded by 20 years of deregulation. And the explanation? Too much regulation! A billion dollars in loans to minorities must explain the 2 trillion dollar problem!

There's nothing wrong with thinking a free market's the way to go for a given problem, provided you got there by engaging your brain rather than taking it on faith. Once you do that, you might find yourself thinking things like "Hm, maybe capital gains should be taxed as ordinary income", or "Hey, turns out it's mathematically impossible to balance the budget by cutting domestic discretionary spending".

Re: Markets are Efficient if and Only if P = NP

#26
post #8

Earlier quoted context omitted.

Was the fall of 2008 "extremely close" to optimal? I'd submit that worldviews based on 1-dimensional criteria like "market!" or "hayek!" fall pretty far short of the mark. Although I can see the attraction. It's nice to simplify things to a level where a human being can actually have the answers with a high degree of confidence. Both the tea-party-hayekians and the linked paper fall into this trap.. what about inform…

Was the fall of 2008 "extremely close" to optimal? Home prices crashed and then more or less stabilized. So yeah, I'd say the crash was close to an optimal price correction. http://research.stlouisfed.org/fred2/series/SPCS20RSA?rid=19... I'm a little confused how why you would believe people who follow Hayek are unfamiliar with questions of information asymmetry and borked incentives. After all, don't they form the b…

I'm confused because everyone who follows Hayek seems to have the solution in hand before they've even heard the problem statement, and that solution doesn't acknowledge those concerns.

I've never heard a self-proclaimed Hayek follower (note that word, follower not thinker) say "I'm worried that the private sector doesn't arrive at the correct incentives in this case" about anything, ever. That's why I'm confused.

Re: Markets are Efficient if and Only if P = NP

#28

Since politicians have no business trying to solve NP problems, perhaps we'd better deregulate the market.

Been there, done that, bought the recession. Regulation, of course, isn't "solving the NP problem", it's modifying the boundary conditions to prevent the system from getting too far out of whack.

Re: Markets are Efficient if and Only if P = NP

#29
post #8

Earlier quoted context omitted.

While I'm pretty much a free-market zealot, I'm also a Hayek groupie. It seems to me that Hayek's work should show us that markets approach perfect efficiency. Because the market is a hideously complex system that only produces its information as an evolved, emergent system, then it is likely that its output is not precise but only extremely close to optimal.

Was the fall of 2008 "extremely close" to optimal? I'd submit that worldviews based on 1-dimensional criteria like "market!" or "hayek!" fall pretty far short of the mark. Although I can see the attraction. It's nice to simplify things to a level where a human being can actually have the answers with a high degree of confidence. Both the tea-party-hayekians and the linked paper fall into this trap.. what about inform…

As much fun as the other reply is, the real defense against your point is that "efficient" doesn't mean what you think it does. Efficiency in a market means that there exist no long-term arbitrage opportunities, because they will be exploited and thus cause prices to shift until those no longer exist. It emphatically DOES NOT mean "good" or "desirable" or anything like that. The market very efficiently went over a cliff, efficiently responding to incentive misalignments created by government regulation and efficiently ensuring that you had no significant arbitrage opportunities in the meantime.

The free market is more force of nature than construct of man, like gravity or a huge river. It can be harnessed, but it will efficiently crush you if you get in its way. It is also like the forces of nature in that it is extremely difficult to successfully harness it when one willfully chooses to not understand it because one does not "like" it, which is why the track record of social systems that start out with "Let's pretend the market isn't a force of nature but that we can will it into compliance with our ideology" tend to fare so poorly in practice; it's hardly any different than assuming gravity won't actually hurt you if you just love hard enough, then trying to get into rocket design. (The problem isn't that you won't get a rocket off the ground with such a plan, the problem is that you will....)

Re: Markets are Efficient if and Only if P = NP

#30
post #8

Earlier quoted context omitted.

While I'm pretty much a free-market zealot, I'm also a Hayek groupie. It seems to me that Hayek's work should show us that markets approach perfect efficiency. Because the market is a hideously complex system that only produces its information as an evolved, emergent system, then it is likely that its output is not precise but only extremely close to optimal.

Was the fall of 2008 "extremely close" to optimal? I'd submit that worldviews based on 1-dimensional criteria like "market!" or "hayek!" fall pretty far short of the mark. Although I can see the attraction. It's nice to simplify things to a level where a human being can actually have the answers with a high degree of confidence. Both the tea-party-hayekians and the linked paper fall into this trap.. what about inform…

I would say the fall of 2008 was pretty close to optimal, especially in terms of what Heyek would predict.

That is not to say it was good for the population, but it was a reasonably efficient reaction to the information the market had about the state of affairs. Note that it didn't fully reflect the entire state of affairs because the market did not have sufficient information, and still doesn't. (I think if it did, the S&P 500 would be about half where it is now.)

The thing that makes me listen to people like Mises and Heyek is that other people who follow their teachings were telling me in 2001 that there would be a housing boom and bubble, and that it would crash eventually due to the inevitable excesses of a bubble. I researched this hypothesis and decided I agreed with it. This made it very easy for me to watch housing prices go up, profit from it, notice when things were ready to change, and then profit from the change.

I think the question of whether markets are efficient or not is one that is placed in a vacuum and thus meaninglesss. Is the market more efficient than government? Yes, always. (It is impossible for a central planner to have sufficient information to set prices correctly.)

Were there people who had the same information as I did, but lacked the economic perspective that I did and thus made bad investments? Yes there were. This is happening today, in fact. We have politicians saying a lot of economically silly things, and the market reacts to this "information".

The question of market efficiency ignores the issue of perspective. You can talk about information asymmetry, and people can debate the amount to which it exists, but I'm absolutely certain that there is perspective asymmetry. I'm going to make a killing in the markets simply because so many people's perspective of economics comes from people like Krugman.

Is that efficient? Maybe-- the markets reflect the perspective of most people, even though they are wrong. But I don't really care.

I'd love it if I couldn't profit from this perspective asymmetry... the benefits to society would far outweigh the profits I'd loose from not being able to bet on these sure things. But so long as people will continue to roll their eyes when an austrian is mentioned, I'll take my profits as a consolation prize.

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