Taking a look at the Sortino ratio, it is a close cousin of the Sharpe ratio. If you need more information on the Sharpe ratio, check out the equities center on Macroaxix. This ratio has the ability to pick apart the potential negative volatility from the general volatility of the market.
When you have a portfolio, it is important to measure the amount of risk that is included in your portfolio. This ratio is beneficial if you are trying to evaluate the amount of negative risk may be in an investment. What this ratio also uses is standard deviation to the downside.
With each ratio you have to understand what factors go into it and what makes it tick because you may find it is not addressing the appropriate parts of your investing or trading.
Once you find the end number, you want the ratio to be as high as possible, as this indicates that the returns are being earned with more efficiency. You may see higher returns with one fund, but the effenciency with which they are being earned may create more risk.
Investing is a balancing act between risk and return, and once you find your sweet spot you can begin to optimize other areas of your investing portfolio. Be sure to test this and know this ratio inside and out before implementing this into your current setup.