Value at Risk – the dangers within
The Bank of England warned earlier this year about the propensity of banks to rely on Value at Risk (VaR) models to manage and guide them on risks. We have been here before, for example during the 1990’s Russian Crisis. Almost exactly the same thing happened, at least on the market side. The was a liquidity crunch as everybody rushed to the exit at the same time.
When everybody rushes to the exit at the same time, one side of the bargain (the buy bit) disappears, and therefore the price formation process is seriously out of whack. When that happens, even small movements in price can and do influence volatility and correlations disproportionately.
Now usually, you are ok to measure your VaR at daily intervals and you don’t update your correlation matrices more than weekly (if you are extremely particular, generally, you can go for 3 months without needing to change, market micro-structures do not change that fast). But as we know, markets have fat tails. Extreme events happen at a far greater frequency than what your normal distribution will suggest.
Consequently, what your VaR numbers will be telling you will not be an accurate reflection of the actual situation. In other words, these numbers tell you the risk that you are carrying. But if you decide to act on that risk number, you will find that the market does not support the consequent decision because there is simply nobody out there to offload your risk to. If nobody wants to purchase your debt or paper, then what are you going to do? You simply suck it up. Or you pray to the great gods of the central banks to provide you with some liquidity.
There is another problem and I quote from the FT article:
In the current environment, no bank chief executive who hopes to hang on to that job can afford to give regulators or shareholders the impression that they are being cavalier about risk. And since VAR is often used to define what level of margins – or financial buffers – are set against trades, some banks are doubly keen to cut VAR, to reduce pressure on their own balance sheets.
But as the banks embark on this task, some are finding themselves caught in an unpleasant trap. The easiest way to reduce a risk exposure is to sell risky assets, such as risky loans. In recent weeks, many banks have been trying to do precisely that.
But these sales have been occurring on such a large scale that they have pushed up market volatility. Thus, measured VAR has risen, exactly as the Bank warned all those months ago.
One big investment bank has recently analysed the impact of its own recent asset sales. These suggest that while these sales should have cut VAR by half in recent weeks on constant volatility levels, in practice this gain was more than wiped out by ensuring market price swings.
By scurrying to reduce risk, in other words, the banks may end up simply running to stand still.
The only way to resolve this is by having stringent stress testing or scenario analysis running. But very few banks that I know of have management trip wires or even have management who take action based upon these stress scenario’s. But all I can predict at this moment is that we will again have this issue. See my previous post on Carnegie as an example.
All this to be taken with a grain of piquant salt!!!
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