Beta equation

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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
Copyright © 2012, Campbell R. Harvey. All Rights Reserved.

Beta Equation

A way to calculate beta, which is the measure of a security's volatility relative to that of the wider market. There are several different beta equations.
Farlex Financial Dictionary. © 2012 Farlex, Inc. All Rights Reserved
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Therefore, standard beta equations for this industry in which DFL is implicitly assumed exogenous would suffer from serious simultaneous-equation bias.
To summarize, a statistically significant coefficient on DOL (or DFL) in a beta equation is not a reliable evidence to support the underlying hypothesis that either variable has caused changes in beta.