Risk adjusted reward 好才是真成功.
In finance, the Sharpe ratio (also known as the Sharpe index, the Sharpe measure, and the reward-to-variability ratio) measures the performance of an investment such as a security or portfolio compared to a risk-free asset, after adjusting for its risk.
Since its revision by the original author, William Sharpe, in 1994,[2] the ex-ante Sharpe ratio is defined as:
![{\displaystyle S_{a}={\frac {E[R_{a}-R_{b}]}{\sigma _{a}}}={\frac {E[R_{a}-R_{b}]}{\sqrt {\mathrm {var} [R_{a}-R_{b}]}}},}](https://wikimedia.org/api/rest_v1/media/math/render/svg/e4e9275387f0d8268289e152b3da43671aae171c)
where 
![{\displaystyle E[R_{a}-R_{b}]}](https://wikimedia.org/api/rest_v1/media/math/render/svg/aa08600a0263abb71ca7bbc7c0c2bfc8412d20c8)
The ex-post Sharpe ratio uses the same equation as the one above but with realized returns of the asset and benchmark rather than expected returns; see the second example below.
The information ratio is a generalization of the Sharpe ratio that uses as benchmark some other, typically risky index rather than using risk-free returns.
