Portfolio homogeneity and systemic risk of financial networks

The present study argues that systemic risk can be understood from two different perspectives, the homogeneity of asset portfolios held by different financial institutions and contagion mechanism. Existing works only emphasize contagion as the basic mechanism of financial crisis. Portfolio homogeneity increases the positive correlations among institutions and therefore the probability of simultaneous collapses of a considerable part of the network. When the contagion was fairly weak, a high portfolio homogeneity would lead to high systemic risk. But, if the contagion is considerably strong, the systemic risk would quite likely be negatively correlated to portfolio homogeneity.