The Symmetric Downside-Risk Sharpe Ratio and the Evaluation of Great Investors and Speculators

The Sharpe ratio is a very useful measure of investment performance. However, it is based on mean-variance theory and thus is basically valid only for quadratic preferences or normal distributions. Hence skewed investment returns can lead to misleading conclusions. This is especially true for superior investors such as Warren Buffett and others with a large number of high returns. Many of these superior investors use capital growth wagering ideas to implement their strategies which leads to higher growth rates but also higher variability of wealth. A simple modification of the Sharpe ratio to assume that the upside deviation is identical to the downside risk provides a useful modification that gives more realistic results.