In this talk we examine the temporal evolution of the e-Mid interbank market transactions and quantify topological changes of the resulting credit network at or near events that where considered pivotal in the 2007-2008 credit crisis.

In order to compare the evolution of network metrics when the size and composition of the underlying network changes over time it becomes crucial to define appropriate network null models against which the statistical significance of such metrics can be assess. Given the directed and weighted nature of our connections we construct a randomised ensemble of networks using the edge swap procedure, but conserving the vertex in-out strength sequence. We compare the topological measure in the real networks with the ones calculated in reshuffled networks. Quantities that are preserved in the randomised ensemble can be traced back/explained as consequences of the changing system composition. Changes not shared by the randomised sample can be associated with changes in banks behavioural choice

The main question we address is whether banks behaviour regarding the choice of counter parties in a trade changed before and during the subprime crisis. In particular, using a network based entropy measure, we assess the level of randomness in the weights distribution across the links of the credit network. We interpret this randomness as a proxy of the level of trust among credit institution.

Finally we assess the impact of a number of network metrics on the spreads paid by banks.