Correlation and diversification:
“There are ways to structure your trades so that you can produce a whole bunch of uncorrelated bets. You have to start with your goal. My goal is that I want to trade more than 15 uncorrelated assets. You are just telling me your problem, and it’s not an insurmountable problem. I strive for approximately 100 different return streams that are roughly uncorrelated to each other. There are cross-correlations that enter into it, so the number works out to be less than 100, but it is well over 15. Correlation doesn’t exist the way most people think it exists. People think that a thing called correlation exists. That’s wrong. What is really happening is that each market is behaving logically based on its own determinants, and as the nature of those determinants changes, what we call correlation changes. For example, when economic growth expectations are volatile, stocks and bonds will be negatively correlated because if growth slows, it will cause both stock prices and interest rates to decline. However, in an environment where inflation expectations are volatile, stocks and bonds will be positively correlated because interest rates will go up with higher inflation, which is detrimental to both bonds and stocks. So both relationships are totally logical, even though they are exact opposites of each other. If you try to represent the stock/bond relationship with one correlation statistic, it denies the causality of the correlation. Correlation is just the word people use to take an average of how two prices have behaved together. When I am setting up my trading bets, I am not looking at correlation; I am looking at whether the drivers are different. I am choosing 15 or more assets that behave differently for logical reasons. I may talk about the return streams in the portfolio being uncorrelated, but be aware that I’m not using the term correlation the way most people do. I am talking about the causation, not the measure.”