The Sharpe Ratio, is a ratio developed by Nobel laureate William F. Sharpe to measure risk-adjusted performance.
This measurement is very useful because although one portfolio or fund can reap higher returns than its peers, it is only a good investment if those higher returns do not come with too much additional risk. The greater a portfolio's Sharpe ratio, the better its risk-adjusted performance has been. A negative Sharpe ratio indicates that a risk-less asset would perform better than the security being analyzed. A variation of the Sharpe ratio is the Sortino ratio.