A measure of an investment's sensitivity to market movements. The beta of the market is 1.00 by definition. Calculated by comparing the investment's excess return over Treasury bills (deemed a risk-free asset for purposes of this calculation) to the market's excess return over Treasury bills. When calculating beta, the market is often represented by different indices depending on how an investment manager benchmarks the investment in question. A beta of 1.10 indicates that the investment is more sensitive to market movements, whereas a beta of 0.85 indicates that the investment is less sensitive than the market.