Measure for assessing the sensitivity of shares or a portfolio to the market as a whole. A beta of 0.5, for example, means that an increase in the market by 10% is expected to lead to a price increase of 5% for the share in question on a long-term average. If the beta is greater than 1, the share is expected to fluctuate more than the market. Shares with a beta of less than 1 therefore carry a lower risk than the market.