What is the Sortino Ratio?

Frank Sortino, now the director of a pension research institute in San Francisco, developed the Sortino Ratio. Many global Mutual Fund rating agencies prefer this risk-adjusted return measure over the Sharpe Ratio, because it is simple and easy. The Sortino Ratio is similar to the Sharpe Ratio, except that instead of using standard deviation as the denominator, it uses downside deviation. The Sortino Ratio was developed to differentiate between good and bad volatility in the Sharpe Ratio. If a fund is volatile to the upside (which is generally a good thing) its Sharpe ratio would still be low.