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A Joke from A Mathematician Plays The Stock Market (I think): Two Efficient Market theorists were walking down the street and see a $100 bill lying there. The

A Joke from A Mathematician Plays The Stock Market (I think): Two Efficient Market theorists were walking down the street and see a $100 bill lying there. They both keep on walking and one says to the other "If that was real, someone would have picked it up by now."

tempestn 12y ago
Funny, but if you think about it... if I had followed that exact principle for my entire life and never picked up $100 bills I saw lying on the street, I think I would be exactly as wealthy as I am now. Even if I never picked up street money at all, it would be pretty close. And I expect I have walked in plenty of places where money has been dropped, but the vast majority of the time, it has been picked up before I can get there. Add in the possibility of dropped money being booby-trapped, and I figure never picking up street money would be a very sensible habit.
Symmetry 12y ago
That's funny but there are actually several forms of the EMH. Strong from: There are no $100 bills on the ground. Semi-Strong: By the time you hear about a $100 bill on the ground someone has already taken it. Weak form: You cannot predictably find $100 bills on the ground.
- RickHull 12y ago
  Another useful way to apply EMH to the real world, especially considering that real world markets are not perfectly efficient, is in terms of asymptotic behavior, hyperbolas, mathematical limits. Paradoxically, Warren Buffett's investing performance, far from being a counterexample to EMH, plays an integral part in the drive towards perfect efficiency. But this drive will never be completed. It's very easy and common to make the leap from EMH, a purely theoretical construct, to asserting that real world markets are perfectly efficient and must therefore behave as EMH entails. This view is mistaken, and the author merely knocks down a straw man with the Buffett counterexample. Instead, in order to use EMH in the real world, one must first judge the efficiency of the market in question. The broadest, deepest, most active and open markets are the most efficient, which is why "the stock market" (in the US) is a favorite example and testing ground. The idea is not that it's perfectly efficient but that it's the most efficient we can access. The real question is: is it efficient enough for efficiency effects to dominate? A fair view of the evidence (i.e. not hunting for or cherry-picking counterexamples) suggests that efficiency effects do dominate. EMH is really about the futility of systematic approaches to achieving excess returns. It was conceived (in some part) as a general refutation to systematic investment proposals. Systems could range in sophistication from always bet on black to virtual Warren Buffett. Only where the system sophistication exceeds (in some sense) the current market efficiency is it able to collect. Soon the unsophisticated have no chips, and the efficiency rises accordingly. The bar is raised, over and over, chewing up new challengers and enshrining champions. That some real world markets are subject to EMH effects also explains the cliché about the highly paid fund manager who performs no better than a dart-throwing monkey. If you find this idea appealing yet EMH is icky, you should check your priors.

tempestn 12y ago

Funny, but if you think about it... if I had followed that exact principle for my entire life and never picked up $100 bills I saw lying on the street, I think I would be exactly as wealthy as I am now. Even if I never picked up street money at all, it would be pretty close. And I expect I have walked in plenty of places where money has been dropped, but the vast majority of the time, it has been picked up before I can get there. Add in the possibility of dropped money being booby-trapped, and I figure never picking up street money would be a very sensible habit.

Symmetry 12y ago

That's funny but there are actually several forms of the EMH. Strong from: There are no $100 bills on the ground. Semi-Strong: By the time you hear about a $100 bill on the ground someone has already taken it. Weak form: You cannot predictably find $100 bills on the ground.

RickHull 12y ago
Another useful way to apply EMH to the real world, especially considering that real world markets are not perfectly efficient, is in terms of asymptotic behavior, hyperbolas, mathematical limits. Paradoxically, Warren Buffett's investing performance, far from being a counterexample to EMH, plays an integral part in the drive towards perfect efficiency. But this drive will never be completed. It's very easy and common to make the leap from EMH, a purely theoretical construct, to asserting that real world markets are perfectly efficient and must therefore behave as EMH entails. This view is mistaken, and the author merely knocks down a straw man with the Buffett counterexample. Instead, in order to use EMH in the real world, one must first judge the efficiency of the market in question. The broadest, deepest, most active and open markets are the most efficient, which is why "the stock market" (in the US) is a favorite example and testing ground. The idea is not that it's perfectly efficient but that it's the most efficient we can access. The real question is: is it efficient enough for efficiency effects to dominate? A fair view of the evidence (i.e. not hunting for or cherry-picking counterexamples) suggests that efficiency effects do dominate. EMH is really about the futility of systematic approaches to achieving excess returns. It was conceived (in some part) as a general refutation to systematic investment proposals. Systems could range in sophistication from always bet on black to virtual Warren Buffett. Only where the system sophistication exceeds (in some sense) the current market efficiency is it able to collect. Soon the unsophisticated have no chips, and the efficiency rises accordingly. The bar is raised, over and over, chewing up new challengers and enshrining champions. That some real world markets are subject to EMH effects also explains the cliché about the highly paid fund manager who performs no better than a dart-throwing monkey. If you find this idea appealing yet EMH is icky, you should check your priors.