The emergence of interbank exposure networks: an empirical analysis and game theoretical models

This thesis studies the emergence of financial exposures between banks and introduces a novel game of financial network formation. It shows empirically that governance structures influence how banks use the interbank market to manage liquidity and that strategic factors are additional drivers of interbank lending for private banks (Ch. 2). It further develops a model of optimal bank behaviour in the absence of liquidity shocks considering the effect of an exogenous bailout probability (Ch. 3), and introduces a model of endogenous liquidity co-insurance formation (Ch. 4). The first chapter, The Purpose of Interbank Markets, tests competing theories of interbank lending using 43 quarters (2002-2012) of confidential data on the German banking sector and interbank market. It shows that banks use the interbank market for liquidity co-insurance as traditionally assumed. However, the importance of the liquidity management function is higher for regionally-focused credit cooperatives and savings banks than for private commercial banks. A distinct effect for private banks is identified; for private banks, increases in interbank liabilities are shown to correlate with a proxy for the bailout probability of banks. The chapter thus offers empirical support for an emerging literature on strategic behaviour in interbank markets and highlights the need to extend the traditional model of liquidity co-insurance. The second chapter, The Emergence of Interbank Exposures, develops a model showing that, even in the hypothetical absence of liquidity shocks, under some conditions the presence of conditional liability guarantees can lead to interbank exposures as an equilibrium outcome. It shows that such an equilibrium is characterised by banks of different sizes and asymmetric bank behaviour. Some banks are active only as lenders with others investing in a productive technology while borrowing in the interbank market. An equilibrium interbank rate is derived which depends on parameters characterising the bailout probability, including different parameters of government behaviour. The third chapter, Coordination and Competition in the Formation of Financial Networks, introduces a generalisation and extension of the seminal work of Allen and Gale (2000). It studies liquidity co-insurance between deposit-taking banks in an n-region economy. Both a static and a dynamic model of the endogenous formation of interbank liquidity co-insurance links are examined. Using a novel approach to model liquidity co-insurance, it is shown that contrary to previous findings it is not possible for banks with limited information to insure optimally against liquidity shocks. However, in a dynamic formulation of the model with best-response dynamics and learning, socially optimal insurance is an evolutionary stable equilibrium. The chapter also studies an extension to the model that introduces non-zero bailout probabilities, which endogenously leads to interbank networks consistent with the structure of interbank exposure networks documented empirically.