Beta = 1 Does a Better Job than Calculated Betas
University of Navarra - IESE Business School
Vicente J. Bermejo-Boixareu
Universidad Carlos III
January 30, 2013
We compute the correlations of the annual stock returns (1989-2008) of the Dow Jones companies with a) Beta Rm; and with b) Rm; and find that the second correlation (assuming beta = 1 for all companies) is higher than the first one, on average, and for all companies except Caterpillar and General Motors. Rm is the return of the S&P 500. Beta = 1 works better than calculated betas!
Not surprisingly, Adjusted betas (0.67 calculated beta 0.33) have higher correlation than calculated betas. But Adjusted betas have lower correlation than beta = 1.
We do the exercise with 4 calculated betas every year end vs. the S$P 500, using: a) monthly data of last 5 years; b) monthly data of last 2 years; c) weekly data of last 5 years; d) daily data of last 5 years. We find similar results with the four betas.
Despite this results, Fernandez (2009) reports that 97.3 % of the professors that justify the betas use regressions, webs, databases, textbooks or papers (the paper specifies which ones), although many of them admit that calculated betas “are poorly measured and have many problems”. Only 0.9% of the professors justified the beta using exclusively personal judgement.
Number of Pages in PDF File: 17
Keywords: beta, historical beta, calculated beta, adjusted beta, common sense
JEL Classification: G12, G31, M21working papers series
Date posted: May 19, 2009 ; Last revised: February 4, 2013
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