EA wrote:While my real investing is just passive investment in index funds, I gather that stock traders don't simply speculate in future value of a company based on its fundamentals, but also try to project the behavior of the crowd to get a step ahead. If you think a crowd is going to overvalue or undervalue something relative to its "real" worth, it's still in your interest to buy or sell accordingly.
This IS speculating based on fundamentals. If a market is driving the price of Microsoft past the point where its price to earning ratio is justified, then you're going to short the stock. If you have a trading scheme based on crowd psychology, you believe you know how the crowd moves, then you would take more of an agnostic stance toward what the price "should" be, such as when doing technical analysis. There are volume trading schemes, where volume indicates an intense interest in the stock. Noise trading broadly describes these activities. If you bet based on crowd psychology, then while inefficiency may be implied, you're more agnostic to that, and simply interested in the equations or common sense intution that describes the direction of the crowd. To illustrate the point, a crowd could maintain a price well above the real worth of the stock for years -- in the inefficient market most people believe describes reality -- but a fundamental analyst would lose his shirt because the "real worth" has to manifest manifest itself within the bounds of his short sale, in my example. A crowd psychologist doesn't care where ground zero is, as long as he can predict the direction of the crowd, he can make money.
EA wrote:That behavior can and should create more wild swings in price due to prediction feedback loops.
Here's one description:
Investopedia wrote:Studies have found that mutual fund inflows are positively correlated with market returns. Momentum plays a part in the decision to invest and when more people invest, the market goes up, encouraging even more people to buy. It's a positive feedback loop.
Read more:
http://www.investopedia.com/articles/07 ... z2F8QSKeIx(don't forget to pick up the FOREX trading essentials book advertised next to the sentence I quoted :)
The argument against this is covered under weak efficiency, the random walk, that argues technical analysis doesn't work because it's easy to do. Since behavioral economics is more recent and I haven't read a great deal about it, I'd have to do some research to see if behavioral trading schemes are all considered to fall under weak efficiency, I'm guessing yes, for now.
To argue against what I just wrote, take the case of a bubble. Efficiency says bubbles shouldn't happen, yet, it's trivial to demonstrate that when the market as a whole tanks over several weeks, that the prices of stocks begin to correlate with each other, which violates the random walk. This doesn't demand that efficiency is false, but it's a serious challenge to the theory. Less serious are isolated instances of "feedback loops" of individual stocks and so on left without arbitrage because of the possibility of seeing faces in a cloud. Anyway, as I've said in a previous post where the crash is considered, here you have these massive, obvious prices correlations, but for all of those who have claimed to predicted the crash, it's interesting to read about some of those who didn't. Warren Buffett testified before congress that he didn't see it coming. He joked that if he had, he would have taken options positions. Warren Buffett is the single best argument against market efficiency. He testified that he rejects market efficiency. Market efficiency's over-arching test is that you can't beat the market, and Warran Buffett didn't beat the market in the single most obvious example of mob psychology that everyone cites as falsifying efficiency. Just something to think about -- it's a very challenging problem for everyone.
If behavioral economics takes over and becomes the new paradigm, this raises some big question. For one, if market participants all become educated in how markets behaves, then they'll correct the market, eliminating the "irrational" behavior. If the new behavioral model leaves the market fundamentally uncorrectable, which is a possibility, then this is bad news for libertarians. What it means is the situation is similar to my last post to Analytics, in that scenario, the wolves perpetually feed on the flock. It may be in our interest to regulate markets much more than we are currently doing, or even government to play a primary role in how capital allocations are made. The trader/liberal position that Analytics takes, even though I disagree with it, can be entirely consistent, more consistant than the common conservative positions are.