The structure and dynamics of multilayer networks

Many ``real-world'' networks are clearly defined while most ``social'' networks are to some extent subjective. Indeed, the accuracy of empirically-determined social networks is a question of some concern because individuals may have distinct perceptions of what constitutes a social link. One unambiguous type of connection is sexual contact. Here we analyze data on the sexual behavior of a random sample of individuals, and find that the cumulative distributions of the number of sexual partners during the twelve months prior to the survey decays as a power law with similar exponents $\alpha \approx 2.4$ for females and males. The scale-free nature of the web of human sexual contacts suggests that strategic interventions aimed at preventing the spread of sexually-transmitted diseases may be the most efficient approach.

The Web of Human Sexual Contacts

We provide a framework for studying the relationship between the financial network architecture and the likelihood of systemic failures due to contagion of counterparty risk. We show that financial contagion exhibits a form of phase transition as interbank connections increase: as long as the magnitude and the number of negative shocks affecting financial institutions are sufficiently small, more "complete" interbank claims enhance the stability of the system. However, beyond a certain point, such interconnections start to serve as a mechanism for propagation of shocks and lead to a more fragile financial system. We also show that, under natural contracting assumptions, financial networks that emerge in equilibrium may be socially inefficient due to the presence of a network externality: even though banks take the effects of their lending, risk-taking and failure on their immediate creditors into account, they do not internalize the consequences of their actions on the rest of the network.

https://papers.ssrn.com/sol3/Delivery.cfm/SSRN_ID2500504_code1428438.pdf?abstractid=2207439&mirid=5&type=2

Systemic Risk and Stability in Financial Networks

This paper develops an analytical model of contagion in financial networks with arbitrary structure. We explore how the probability and potential impact of contagion is influenced by aggregate and idiosyncratic shocks, changes in network structure, and asset market liquidity. Our findings suggest that financial systems exhibit a robust-yet-fragile tendency: while the probability of contagion may be low, the effects can be extremely widespread when problems occur. And we suggest why the resilience of the system in withstanding fairly large shocks prior to 2007 should not have been taken as a reliable guide to its future robustness.

https://papers.ssrn.com/sol3/Delivery.cfm/SSRN_ID1577043_code459244.pdf?abstractid=1577043&mirid=1

Contagion in Financial Networks

This paper argues that the extent of financial contagion exhibits a form of phase transition: as long as the magnitude of negative shocks affecting financial institutions are sufficiently small, a more densely connected financial network (corresponding to a more diversified pattern of interbank liabilities) enhances financial stability. However, beyond a certain point, dense interconnections serve as a mechanism for the propagation of shocks, leading to a more fragile financial system. Our results thus highlight that the same factors that contribute to resilience under certain conditions may function as significant sources of systemic risk under others. (JEL D85, E44, G21, G28, L14)

/pdf/systemic-risk-and-stability-in-financial-networks-ecudzsz6lj.pdf

Systemic risk and stability in financial networks

We provide an empirical analysis of the network structure of the Austrian interbank market based on Austrian Central Bank (OeNB) data. The interbank market is interpreted as a network where banks are nodes and the claims and liabilities between banks define the links. This allows us to apply methods from general network theory. We find that the degree distributions of the interbank network follow power laws. Given this result we discuss how the network structure affects the stability of the banking system with respect to the elimination of a node in the network, i.e. the default of a single bank. Further, the interbank liability network shows a community structure that exactly mirrors the regional and sectoral organization of the current Austrian banking system. The banking network has the typical structural features found in numerous other complex real-world networks: a low clustering coefficient and a short average path length. These empirical findings are in marked contrast to the network structures th...

Network topology of the interbank market

We propose a new approach to assess the financial stability of an entire banking system using standard tools from modern risk management in combination with a network model of inter-bank loans. Rather than looking at banks individually, we analyze risk at the level of the banking system as a whole. We apply our model to a unique dataset of all Austrian banks. We find that correlation in banks' asset portfolios dominates contagion as the main source of systemic risk. Contagion occurs rarely but can wipe out a major part of the banking system. Low bankruptcy costs and an efficient crisis resolution policy are crucial to limit the system wide impact of contagious default events. We compute the "value at risk" for a lender of last resort and find the necessary funds to prevent contagion to be surprisingly small. More diversification in the inter-bank market does not necessarily reduce the risk of contagion.

/pdf/risk-assessment-for-banking-systems-42m67950km.pdf

Risk Assessment for Banking Systems

We propose a new approach to assess systemic financial stability of a banking system using standard tools from modern risk management in combination with a network model of interbank loans. We apply our model to a unique data set of all Austrian banks. We find that correlation in banks' asset portfolios dominates contagion as the main source of systemic risk. Contagion is rare but can nonetheless wipe out a major part of the banking system. Low bankruptcy costs and an efficient crisis resolution policy are crucial to limit the systemwide impact of contagious default events. We compute the “value at risk” for a lender of last resort and find that the funds necessary to prevent contagion are surprisingly small.

/pdf/risk-assessment-for-banking-systems-ph1f3rxpir.pdf

We propose a new method for the analysis of systemic stability of a banking system relying mostly on market data. We model both asset correlations and interlinkages from interbank borrowing so that our analysis gauges two major sources of systemic risk: Correlated exposures and mutual credit relations that may cause domino effects. We apply our method to a dataset of the 10 major UK banks and analyze insolvency risk over a one year horizon. We also suggest a stress testing procedure by analyzing the conditional asset return distribution that results from the hypothetical failure of individual institutions in this system. Rather than looking at individual bank defaults ceteris paribus, we take the change in the asset return distribution and the resulting change in the risk of all other banks into account. This takes previous stress tests of interlinkages a substantial step further.

/pdf/using-market-information-for-banking-system-risk-assessment-19ef37fhg8.pdf

Using Market Information for Banking System Risk Assessment

We propose a new method for the analysis of systemic stability of a banking system relying mostly on market data. We model both asset correlations and interlinkages from interbank borrowing so that our analysis gauges two major sources of systemic risk: correlated exposures and mutual credit relations that may cause domino effects of insolvencies. We apply our method to a data set of the ten major UK banks and analyze insolvency risk over a one-year horizon. We also suggest a stress-testing procedure by analyzing the conditional asset return distribution that results from the hypothetical failure of individual institutions in this system. Rather than looking at individual bank defaults ceteris paribus, we take the change in the asset return distribution and the resulting change in the risk of all other banks into account. This takes previous stress tests of interlinkages a substantial step further.

Helmut Elsinger

Papers

Network topology of the interbank market

Risk Assessment for Banking Systems

Risk Assessment for Banking Systems

Using Market Information for Banking System Risk Assessment

Using Market Information for Banking System Risk Assessment