The standard deviation of an investments or portfolios return divided by the...

ratio of a portfolio's standard deviation to the standard deviation of a benchmark . see also R-squared, volatility.

Another statistical measure of fund risk (see also Beta). Volatility is measured by taking the standard deviation of fund returns over several months and dividing it by the standard deviation of returns for the S&P 500 (for stock funds) or the Lehman Aggregate Bond index (for bond funds) over the same period. A fund whose relative volatility is greater than 1.0 is said to be more volatile than the market. Conversely, a volatility rating of less than 1.0 indicates a fund is less volatile than the broad stock or bond market. (see Standard Deviation)

See Risk