90% Rule

Pick up any university textbook on investing and it will tell you that approximately 90% of all of the movement in an individual stock can be attributed to changes in the broader market. Equity research companies such as Standard & Poor’s and Value Line provide their subscribers with a data point called beta. Beta is a correlation coefficient between the stock being reported on and the market, which in most cases is the S&P 500. Take a look at dozen or so stocks from the S&P 500 a...