Does diversification improve the performance of German banks? Evidence from individual bank loan portfolios

Should banks be diversified or focused? Does diversification indeed lead to increased performance and therefore greater safety on the part of banks as traditional portfolio and banking theory would suggest? Recently, Acharya et al. (J Bus, 79:1355-1412, 2006) have found that for Italian banks the answers to these questions depend on the level of risk that a bank has taken. In this paper we investigate whether this result is robust to the choice of the sample and to the calculation of the risk variable. To this end we use a unique data set of the individual bank loan portfolios of 983 German banks for the period from 1996 to 2002 and calculate a Value-at-Risk based risk variable. We then investigate the link between banks' profitability and their portfolio diversification across different industries, broader economic sectors and geographical regions. We find little evidence of large performance benefits associated with diversification: For the majority of our data, diversification tends to be associated with reductions in bank returns, even after controlling for risk. Only in a few cases (e.g., high-risk banks and industrial diversification) do we find statistically significant positive relationships between diversification and bank returns. Our findings contradict both the empirical findings of Acharya et al. (J Bus, 79:1355-1412, 2006) and the theoretical findings of Winton (Don't put all your eggs in one basket? Diversification and specialization in lending. Working Paper No. 00-16, University of Minnesota, 1999). © 2007 Springer Science+Business Media, LLC.