Part of an economic theory for valuing financial securities and calculating the cost of capital, known as the capital asset pricing model, beta measures the sensitivity of the price of a particular asset to changes in the market as a whole. If a company's shares have a beta of 0. 8 it implies that on average the share price will change by 0. 8% if there is a 1% change in the market. There is a long-running debate about whether a beta calculated from a security's past relationship with the market actually predicts how that relationship will behave in future, leading some doubting economists to claim that beta is "dead".