Beta is the measure of an asset’s risk in relation to the market (for example, the S&P500) or to an alternative benchmark or factors. Roughly speaking, a security with a beta of 1.5, will have move, on average, 1.5 times the market return.
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For a whole portfolio, the beta is the weighted sum of the individual asset betas, according to the proportions of the investments in the portfolio. E.g., if 50% of the money is in stock A with a beta of 2.00, and 50% of the money is in stock B with a beta of 1.00,the portfolio beta is 1.50.
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