The quantitative schools of investing rely on very high powered mathematics (often drawing on physics and engineering graduate students). They tread on very dangerous ground (often engaging in complex and highly leveraged speculation) and make errors in assumptions about the market conditions upon which the mathematical models they use to invest are based. Fat Tails and Limitations of Normal Distributions describes one common mistake:
Stock market data clearly shows that a normal distribution does not provide a good model of the market. Not every system is defined by a normal distribution – it is common for distributions to be close to normal but there is no reason any system need be. Many statistical tools have as an underlying assumption that the system in question is a normal distribution (therefore to use the tools you need to determine if the system can be classified that way – if not some tools can’t be used).
Crazy as it seems, very smart people continually forget that the markets often experience panics, euphoria, behave in ways that models do not predict, seize up and fail to function… Against the Gods by Peter Bernstein provides a good picture of the chaotic nature of financial market risks. A good book on an example of a mathematical model failure, Long Term Capital Management: When Genius Failed. Another excellent book on financial market chaos is: Manias, Panics, and Crashes: A History of Financial Crises.
I keep thinking people will learn but so far the faith in numbers seems to outweigh the past examples of overconfident failures.
Related: Data doesn’t lie but you can be fooled – investment risk – Statistics for Experimenters
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Smart people can and do make huge mistakes when investing. While mathematical models provide an interesting framework for investing, if they are used too exactly without thought for other variables, the results can be devistating.
I understand there has been a large move toward using highly complex math for financial strategies. I understand many derivatives and other investment vehicles have been created. I just don’t really get what makes some of it engineering…
Maybe the latest huge bailout will change how things are done. I doubt it. New rules will be put in place. Plenty of people will pay politicians plenty of money to assure their methods of subverting the intent of those rules are allowed to continue…
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