Beta equation (security)


The market beta of a security is determined as follows: Regress excess returns of stock y on excess returns of the market. The slope coefficient is beta. Define n as number of observation numbers.

  • Beta=
  • [(n) (sum of [xy]) ]-[ (sum of x) (sum of y)]/
  • [(n) (sum of [xx]) ]-[ (sum of x) (sum of x)]
  • where: n = # of observations (usually 36 to 60 months)
  • x = rate of return for the S&P 500 index
  • y = rate of return for the security.
  • Related: Alpha

Investing Essentials

Copyright © 2011 Campbell R. Harvey, Professor of Finance, Fuqua School of Business at Duke University

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