bh wrote:Interesting...
http://www.indexfundeducator.com/randomness.htm
So, just by luck, a certain small percentage of mutual fund managers will have great track records. So could you, armed with a coin and the strength to keep flipping. Is it likely, that you, or any one mutual fund manager, will have a great track record over time? No. But, just based on sheer luck, some will and we will call them “genius” and put them on the financial television programs. Is it likely that a manager who “happened” to produce a superior track record one period (say the 1980s) would produce a superior track record in the next period (the 1990s)? Absolutely not! This is borne out by the research. (See the Fallacy of Persistency elsewhere on this web site.) We can not state this strongly enough: the precious touchstone upon which mutual funds stake their claim to fame, superior track record, is, upon proper examination simply “statistical fluke”, with the future track record of the so-called financial expert destined for ordinariness or worse. We are talking here about major ‘distortion’, an entire industry based on statistical confusion and the propensity of investors to be Fooled by Randomness.
This is good too.
http://www.indexfundeducator.com/persistency.htm" onclick="window.open(this.href);return false;
When I was teaching Intro to Finance at Pitt all those years ago, I illustrated market efficiency on these 2 examples:
1) Say that at the beginning of every year, there is 50:50 chance that the market will be up/down at the end of that year. So, the chances that a portfolio manager flipping a coin will be right is 0.50 . The chance that the manager will be right 10 years in a row (and will be considered a true investment star) will thus be 0.5^10 = 0.0009765625
So, there is 1-0.0009765625 = 0.9990234375 that the manager will be wrong at least once. However, the chance that AT LEAST one manager among , say, 5,000 portfolio managers (all flipping coins) will be right is:
(100% less EVERYBODY is wrong) i.e.
1 - (0.9990234375)^5000 = 99.25%
2) I took old WSJ ads for mutual funds claiming substantial market overperformance (Fidelity with Peter Lynch used to advertise a lot this way). Then, I showed the subsequent performance of such funds (after the ad) - it was always much lower than the advertised extra gains.
2)