Beta

The Beta measures the amount that investors expect the stock price to change for each additional 1% change in the market. The average beta of all stocks is 1.0. A stock with a beta lower than 1.0 is unusually insensitive to market movements. A stock with a beta > 1.0 is above average sensitive to market movements.

The formula for beta is:

$\beta _{i}$ = ${\frac {\sigma _{im}}{\sigma _{i}^{2}}}$

Where $\sigma _{im}$ is the Covariance@math between the stocks returns and the market returns and ${\sigma _{i}^{2}}$ is the variance of returns in the market.