Article: James Montier on how CAPM is CRAP
Today's "Outside The Box" piece from John Mauldin's free InvestorsInsight newsletter debunks beta as a useful measure of risk. Beta measures a portfolio's volatility when compared to the market. The article illustrates why beta is a poor measure for risk by using multiple empirical studies. In my own investing, I use a stock's margin of safety as a measure of risk.
In recent months, I've been deciding whether or not I need to calculate a Sharpe Ratio for my portfolio. The Sharpe Ratio is a measure of outperformance normalized by the amount of risk taken and highly regarded by my quant friends. In the end, I decided that I did not want to spend the time to calculate this ratio. My main reason is similar to the reasoning against using beta. Specifically, risk should not be measured by the short-term variance of one's returns. At the same time, I have also decided to measure investing success by maintaining 12% IRR at year-end instead of comparing results with the S&P. Although I will still compare results to the S&P for illustrative reasons, I will not beat myself up if I don't match the S&P. Beating the S&P year-over-year is a game that mutual fund managers need to play to separate a fool from his money.
In recent months, I've been deciding whether or not I need to calculate a Sharpe Ratio for my portfolio. The Sharpe Ratio is a measure of outperformance normalized by the amount of risk taken and highly regarded by my quant friends. In the end, I decided that I did not want to spend the time to calculate this ratio. My main reason is similar to the reasoning against using beta. Specifically, risk should not be measured by the short-term variance of one's returns. At the same time, I have also decided to measure investing success by maintaining 12% IRR at year-end instead of comparing results with the S&P. Although I will still compare results to the S&P for illustrative reasons, I will not beat myself up if I don't match the S&P. Beating the S&P year-over-year is a game that mutual fund managers need to play to separate a fool from his money.