We explore the impact of large banks and of financial openness for aggregate growth. Large banks matter because of granular effects: if markets are very concentrated in terms of the size distribution of banks, idiosyncratic shocks at the bank-level do not cancel out in the aggregate but can affect macroeconomic outcomes. Financial openness may affect GDP growth in and of itself, and it may also influence concentration in banking and thus the impact of bank-specific shocks for the aggregate economy. To test these relationships, we use different measures of de jure and de facto financial openness in a linked micro-macro panel dataset. Our research has three main findings: First, bank-level shocks significantly impact on GDP. Second, financial openness lowers GDP growth. Third, granular effects tend to be stronger in financially closed economies.

Does the mere presence of big banks affect macroeconomic outcomes? In this paper, we develop a theory of granularity (Gabaix, 2011) for the banking sector, introducing Bertrand competition and heterogeneous banks charging variable markups. Using this framework, we show conditions under which idiosyncratic shocks to bank lending can generate aggregate fluctuations in the credit supply when the banking sector is highly concentrated. We empirically assess the relevance of these granular effects in banking using a linked micro-macro dataset of more than 80 countries for the years 1995-2009. The banking sector for many countries is indeed granular, as the right tail of the bank size distribution follows a power law. We then demonstrate granular effects in the banking sector on macroeconomic outcomes. The presence of big banks measured by high market concentration is associated with a positive and significant relationship between bank-level credit growth and aggregate growth of credit or gross domestic product.

Governments often justify interventions into the financial system in the form of bail outs or liquidity assistance with the systemic importance of large banks for the real economy. In this paper, we analyze whether idiosyncratic shocks to loan growth at large banks have effects on real GDP growth. We employ a measure of idiosyncratic shocks which follows Gabaix (forthcoming). He shows that idiosyncratic shocks to large firms have an impact on US GDP growth. In an application to the banking sector, we find evidence that changes in lending by large banks have a significant short-run impact on GDP growth. Episodes of negative loan growth rates and the Eastern European countries in our sample drive these results.

Government interventions into the financial system in the form of bail out operations or liquidity assistance are often justified with the systemic importance of

large banks for the real economy. In this paper, we test whether idiosyncratic

shocks to loan growth at large banks have effects on real GDP growth. We employ

a measure of idiosyncratic shocks which follows Gabaix (2009). He shows that

idiosyncratic shocks at large firms have an impact on GDP growth in the US. We

apply this idea to the banking sector. We find evidence that changes in lending

by large banks have a significant impact on GDP growth. This effect is mostly

driven by episodes of negative loan growth rates and by the Eastern European

countries in our sample.

Size matters in banking. In this paper, we explore whether shocks originating at large banks affect the probability of distress of smaller banks and thus the stability of the banking system. Our analysis proceeds in two steps. In a first step, we follow Gabaix and construct a measure of idiosyncratic shocks at large banks, the so-called Banking Granular Residual. This measure documents the importance of size effects for the German banking system. In a second step, we incorporate this measure of idiosyncratic shocks at large banks into an integrated stress-testing model for the German banking system following De Graeve et al. (2008). We find that positive shocks at large banks reduce the probability of distress of small banks.