The Herfindahl-Hirschman Index (HHI) is a measure of diversification, commonly used as an indicator to calculate banks’ credit concentration risk capital requirements (where credit concentration risk is potential losses from undiversified portfolios). According to BCBS (2019) HHI is employed by c. 50% of regulators, including the Prudential Regulation Authority (PRA) since 2016. However, despite some evidence that the data-light, easy-to-implement HHI produces broadly comparable outcomes with formal models (eg Bundesbank (2006)), such evidence is limited to large banks or theoretical datasets. In this post I examine the relationship between HHI and a formal model of sector and geographical concentration risk. I show that, for a wide sample of bank sizes, HHI is poorly correlated with the model outputs for both risk types.
Marcus Buckmann, Paula Gallego Marquez, Mariana Gimpelewicz and Sujit Kapadia
Bank failures are very costly for society. Following the 2007/2008 global financial crisis, international regulators introduced a package of new banking regulations, known as Basel III. This includes a wider range of capital and liquidity requirements to protect banks from different risks. But could the additional complexity be unnecessary or even increase risks, as some have argued? In a recent staff working paper, we assess the value of multiple regulatory requirements by examining how different combinations of metrics might have helped prior to the 2007/2008 crisis in gauging banks that subsequently failed. Our results generally support the case for a small portfolio of different regulatory metrics: having belts and braces (or suspenders) can strengthen the resilience of the banking system.
The financial crisis exposed banks’ vulnerability to a type of risk associated with derivatives: credit valuation adjustment (CVA) risk. Despite being a major driver of losses – around $43 billion across 10 banks according to one estimate – there had been no capital requirement to cushion banks against these losses. New rules in 2014 changed this.
Last year I published a post arguing that there are two productivity puzzles – one in the level and the other in the growth rate of labour productivity – that contained an error. In the original blog, I showed that we could decompose the puzzle(s!) into contributions from either slower than trend growth in capital services per hour worked (capital deepening) or technology growth (TFP).
In the world of bank capital regulation, minimum requirementsgraballtheheadlines. But actual capital resources are what absorb unexpected losses. Banks and building societies typically hold resources substantially in excess of requirements – called the capital surplus. One reason is to avoid breaching the minimum due to unforeseen shocks. Another is to build resources in anticipation of requirements arising from growth or regulatory change. The chart shows how capital surpluses (on total requirements including Pillars 1 and 2, and all types of capital) have varied in recent decades. It is based on historical data from regulatory returns.