The beta coefficient measures the sensitivity of a stock ' s returns relative to the overall market (usually the S & P 500). A beta of: 1.0 indicates the stock moves in line with the market. Greater than 1.0 suggests the stock is more volatile than the market. Less than 1.0 suggests the stock is less volatile. D is correct because beta specifically compares the volatility of a stock to the market. A is incorrect as beta does not measure the market's volatility. B is incorrect as beta considers both upside and downside movements. C is incorrect as beta does not measure liquidity. Reference: SIE Study Guide, Chapter 6: Portfolio Management