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Published online by Cambridge University Press: 19 October 2009
In the linear market-index model of the return-generating process, return on security j is given by
where αj and βj are constants characteristic of company j, is return on a market index, and
is the company-specific component of return such that
and
. The coefficient βj is given by
. It is known as market responsiveness, volatility, systematic risk, and, more commonly, simply as “beta.” It has been widely accepted as a measure of nondiversifiable risk and incorporated in popular performance measures. Many stock information services now provide estimates of beta.