The Effects of Correlated Jump Risks on Default Correlation

Abstract

The previous theoretical studies on default correlations analyze them only when the firm value moves continuously. Unlike these researches, this paper examines them when the firm value is exposed to jump risks and these jump risks between firms are correlated. Under these conditions, the effects of the correlated jump risks on default correlations are the followings. First, as stated in the previous study, this paper also states that the default correlations increase and then decrease with time. Second, there is a big difference between the existing study and this paper in the aspect of the firms' credit qualities. In the previous study, over a long horizon, default correlations of lower credit qualities of firms are lower than those of higher credit qualities of firms. However, under the jump-diffusion model we are able to obtain the opposite result to the previous study, which is that the jump-diffusion model is consistent with the empirical study in the case of lower credit qualities of firms. Third, on default correlations between the speculative graded firms over a long horizon, this paper is more consistent with the empirical results rather than the previous theoretical study. On contrary, on default correlations between the investment graded firms over a short horizon, the result is completely the opposite. Finally, in contrast to the diffusion model of Merton (1974) where default correlations over a short period are insignificant, default correlations under the jump-diffusion model may be consistent with the empirical results due to correlated jump risks.