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Does idiosyncratic risk matter? Evidence from mergers and acquisitions

Pascal Nguyen (ESDES - Business School, Université Catholique de Lyon, Lyon, France)
Younes Ben Zaied (ISTEC Ecole Superieure de Commerce et de Marketing, Paris, France)
Thu Phuong Pham (University of Adelaide Business School, Adelaide, Australia and IPAG Business School, Paris, France)

Journal of Risk Finance

ISSN: 1526-5943

Article publication date: 27 September 2019

Issue publication date: 15 October 2019




This paper aims to investigate whether idiosyncratic volatility is a priced risk factor in the Australian stock market.


The authors use the change in idiosyncratic volatility around acquisition announcements and the related stock price revaluation to test whether the idiosyncratic risk is priced. If the idiosyncratic risk is priced, increases (decreases) in idiosyncratic volatility should be associated with decreases (increases) in the acquirer’s stock price, as the latter’s future cash flows are discounted at a higher (lower) rate. The sample consists of 2,656 completed acquisitions by Australian listed firms over the period January 1990 to October 2014 for which deal value represents more than 5 per cent of the acquirer’s market value.


Increases (decreases) in idiosyncratic risk are associated with significant decreases (increases) in firm value. This negative relationship is robust to the presence of outliers; is unaffected by the incidence of the 2007-2008 financial crisis; holds using alternative measures of idiosyncratic risk; and is more significant after excluding the resources sector. Firms with a higher idiosyncratic risk prior to the acquisition, and firms avoiding stock to pay for the acquisition, experience a more significant stock price increase in relation to a decrease in idiosyncratic risk.

Research limitations/implications

Considering the small size of the Australian economy, investors may have less scope to mitigate idiosyncratic risk. As a consequence, idiosyncratic risk is associated with the positive excess return, contrary to what standard asset pricing theory assumes. The results support Merton’s (1987) hypothesis that investors are exposed to idiosyncratic risk due to imperfect portfolio diversification and receive compensation for bearing that risk.

Practical implications

The pricing of idiosyncratic risk may also explain why the Australian stock market has historically offered a high equity risk premium. A practical implication would be for international investors to take advantage of the diversification constraints of local investors to capture higher risk premiums and achieve superior returns.


While prior studies demonstrate that stocks with higher idiosyncratic risk are associated with higher subsequent returns, the authors show that an increase in idiosyncratic risk is associated with a decrease in stock prices using acquisition announcements as shocks to a firm’s idiosyncratic risk. In other words, the results arise from within-firm variations rather than from cross-sectional differences in stock returns.



Nguyen, P., Ben Zaied, Y. and Pham, T.P. (2019), "Does idiosyncratic risk matter? Evidence from mergers and acquisitions", Journal of Risk Finance, Vol. 20 No. 4, pp. 313-329.



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Copyright © 2019, Emerald Publishing Limited

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