Economics 19/01/2010: Irish banks - a rational model of risky strategies

I just came across a very interesting paper, written back in November 2007 and published by the Bank for International Settlements as a Working Paper No 238. Authored by Ryan Stever and titled “Bank size, credit and the sources of bank market risk” the paper “…examines bank risk by investigating the equity and loan portfolio characteristics of publicly-traded bank holding companies.” The study is based on the US banks, with sample being a panel of ‘at least 339 publicly trades BHCs at each point in time” for the period of 1986-2003. “These range in size from American Bancorporation at $31 million in book assets (200 employees) to Citigroup at $1.26 trillion (over 280,000 employees).”

“Unlike the pattern for non-financial firms, equity betas of large banks are two to five times greater than those of small banks. In explaining this, we note that regulation imposes an effective cap on banks’ equity volatility. Because the portfolios of small banks are less diversified, this cap has a greater effect on small banks than large banks.”

In other words, there is plenty of evidence that even when effective, regulators can induce some unintended consequences onto the banking system and that these consequences, if unaddressed can lead to systemic failures.

Here is how it works:

• Regulators (and/or shareholders through exercise of their voting rights) place a limit on the total volatility of each bank’s assets regardless of size, which tends to minimize bank risk; however
• Small banks have more idiosyncratic risk inherent in their loan portfolio “because they cannot diversify away idiosyncratic volatility as well as large bank” (practically – smaller banks are more specialized, making their loans books more exposed to idiosyncratic strategy risk).
• Smaller banks inability to diversify comes about in “a number of different ways – for example; less total loans held, less diversity in borrower type (they do not have access to large borrowers) and geographic restrictions (small banks tend to be more localized);

 Because their total equity volatility is limited by regulation smaller banks must then find a way to eliminate their idiosyncratic volatility that is in excess of larger banks’ idiosyncratic volatility. To do this, small banks do not necessarily pursue higher levels of equity capitalization or lending to different sectors in the economy – in other words, they do not strive to become like larger banks, but instead they either:

•  make loans with less credit risk than large banks (Swiss private banks, for example). This has the effect of reducing idiosyncratic volatility (as desired) and also reducing the beta of each loan (and thus the equity beta of small banks); or
• demand more collateral (e.g. Irish banks).
  

Of course, the problem with selecting the latter path (beefing up collateral) as opposed to the penultimate pathway (more conservative, risk-sensitive lending) – as Irish banks should have learned from the current crisis – leads to additional problem, not highlighted in the study. This problem is manifested in the selection bias induced onto collateral – smaller banks opting for higher collateral requirements will take on less diversified collateral that is more likely to be positively correlated with their own (risk-skewed) loans books. Thus collateral risk becomes positively correlated with loans risk.

Just think of what type of collateral Liam Carroll was supplying for his property development loans? You’ve guessed it – property-based collateral.

In fact, the study does find that small banks did not lower their equity volatility through lower leverage. Instead, “the reduced ability of small banks to diversify forces them to either pick borrowers whose assets have relatively low credit risk or make loans that are backed by relatively more collateral.”