The relative volatility of returns earned from holding a specific portfolio of securities. A high portfolio beta indicates securities that tend to be more volatile in their price movements than the market taken as a whole. Portfolio beta is calculated by summing the products of each security's beta times the proportional weight of the security in the portfolio. For example, if a portfolio consists of two securities, one valued at $15,000 and having a beta of 0.9 and the other valued at $10,000 and having a beta of 1.5, the portfolio beta is (0.9)( ^$15,000/_$25,000 ) + (1.5)( ^$10,000/_$25,000 ), or 1.14.