what is beta 
simply put beta is a measure of market risk more precisely it is a measure of the volatility or systematic risk of a security or portfolio compared to the market as a whole in statistical terms it is the slope of the coefficient for a security stock regressed against a benchmark market index s p 500 each of these data points represents an individual stock s returns against those of the market as a whole so beta effectively describes the activity of a security s returns as it responds to swings in the market 