Systemic Risk and Stability in Financial Networks
The Harvard Law School Forum on Corporate Governance and Financial Regulation 2013-04-05
The recent financial crisis has rekindled interest in the relationship between the structure of the financial network and systemic risk. Two polar views on this relationship have been suggested in the academic literature and the policy world. The first maintains that the “incompleteness” of the financial network can be a source of instability, as individual banks are overly exposed to the liabilities of a handful of financial institutions. Thus, according to this argument, a more complete financial network, which limits the exposure of the banks to any one counterparty would be less prone to systemic failures. The second view, in stark contrast, hypothesizes that it is the highly interconnected nature of the financial system that contributes to its fragility, as it facilitates the spread of financial distress and solvency problems from one bank to the rest in an epidemic-like fashion.
In our recent NBER working paper, Systemic Risk and Stability in Financial Networks, my co-authors (Asuman Ozdaglar of MIT and Alireza Tahbaz-Salehi of Columbia Business School) and I provide a tractable theoretical framework for the study of the economic forces shaping the relationship between the structure of the financial network and systemic risk. We show that as long as the magnitude (or the number) of negative shocks is below a critical threshold, a more equal distribution of interbank obligations leads to less fragility. In particular, all else equal, the sparsely connected ring financial network (corresponding to a credit chain) is the most fragile of all configurations, whereas the highly interconnected complete financial network is the configuration least prone to contagion. In line with the observations made by Allen and Gale (2000), our results establish that, in the more complete networks, the losses of a distressed bank are passed to a larger number of counterparties, guaranteeing a more efficient use of the excess liquidity in the system in forestalling defaults.