A measure of a stockÂ’s relative volatility. The Standard & PoorÂ’s 500 Stock Index has a beta coefficient of 1. The beta of individual stocks, mutual funds, or portfolios is measured in comparison to this index. For example, a stock that has a high beta of 1.5 and thus high volatility has 50 percent more movement than the rest of the market. Although high betas can result in strong gains, they also can produce substantial losses. Similarly, stocks with a beta below 1.0 move less than the market as a whole.