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The Impact of News on Measures of Undiversifiable Risk: Evidence from the UK Stock Market

The usual measure of the undiversifiable risk of a portfolio is its beta. Recent research has allowed beta estimates to vary over time, often based on symmetric multivariate GARCH models. There is, however, widespread evidence in the literature that the volatilities of asset returns, in particular those from stock markets, show evidence of an asymmetric response to good and bad news. Using UK equity index data, this paper considers the impact of news on time varying measures of beta. The results suggest that beta depends on two sources of news-news about the market and news about the sector. The asymmetric effect in beta is consistent across all sectors considered. Recent research provides conflicting evidence as to whether abnormalities in equity returns are a result of changes in expected returns in an efficient market or an over-reaction to new information. The evidence in this paper suggests that such abnormalities may occur as a result of changes in expected return caused by time-variation and asymmetry in beta.

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Paper provided by The University of Melbourne in its series Department of Economics - Working Papers Series with number 733.

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Length: 28 pages
Date of creation: 2000
Date of revision:
Handle: RePEc:mlb:wpaper:733
Contact details of provider: Postal: Department of Economics, The University of Melbourne, 4th Floor, FBE Building, Level 4, 111 Barry Street. Victoria, 3010, Australia
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  1. Chopra, Navin & Lakonishok, Josef & Ritter, Jay R., 1992. "Measuring abnormal performance : Do stocks overreact?," Journal of Financial Economics, Elsevier, vol. 31(2), pages 235-268, April.
  2. Robert F. Engle & Victor K. Ng, 1991. "Measuring and Testing the Impact of News on Volatility," NBER Working Papers 3681, National Bureau of Economic Research, Inc.
  3. Henry, O.T.J., 1995. "Modelling the Assymetry of Stock Market Volatility," Department of Economics - Working Papers Series 487, The University of Melbourne.
  4. Lawrence R. Glosten & Ravi Jagannathan & David E. Runkle, 1993. "On the relation between the expected value and the volatility of the nominal excess return on stocks," Staff Report 157, Federal Reserve Bank of Minneapolis.
  5. Bollerslev, Tim & Engle, Robert F & Wooldridge, Jeffrey M, 1988. "A Capital Asset Pricing Model with Time-Varying Covariances," Journal of Political Economy, University of Chicago Press, vol. 96(1), pages 116-31, February.
  6. Braun, Phillip A & Nelson, Daniel B & Sunier, Alain M, 1995. " Good News, Bad News, Volatility, and Betas," Journal of Finance, American Finance Association, vol. 50(5), pages 1575-1603, December.
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