I want to distinguish two issues, as a prelude to another post on central capital calculations.
First, there’s behavior. If everyone, or many folk, do the same thing, then you get herding and the possibility of phase changes. In financial stability terms that’s bad. You want people to do different things, as a diverse ecology of financial institutions is more robust than a mono-culture.
Second, there are standards, like regulatory capital. You want them to be simple and uniformly implemented, because that creates investor trust. There is a massive information asymmetry between bank managers and bank investors, and regulatory capital ratios help to level the playing field. It doesn’t matter if they don’t measure risk very well because you care much more about false negatives (well capitalised bank is not solvent) than false positives (solvent bank does not pass regulatory standard).
Thus, recent objections to my proposal to centralise model-based capital calculations are wrong because they confuse the first issue with the second. SWP says:
We want to diversify model risk, not concentrate it. Centralized calculation concentrates it. I actually see an evolutionary benefit in the wide range of model risk weights that DEM bewails. That represents a diverse ecosystem of entities with divergent views that is less vulnerable to a single shock. Yeah, that shock will crater some banks, but not all of them. When I think of any-ANY-centralized calculation, I think of the Socialist Calculation Debate. I also think of monocultures that are dangerously vulnerable-systemically vulnerable-to a single shock. Think of the devastation that smallpox wreaked on native American populations. A single shock can crater everybody all at once.
That would be true if all banks did the same thing, but there is no requirement, or even strong incentive, for that. All I am asking is that they all, in their diverse ways, meet a simple standard: that centrally calculated market risk RWAs are less than the amount of capital they set aside for market risk.
Will this central calculation be wrong? Yes, clearly so. Will it be differently wrong for different banks? No, it will be wrong in the same way for everyone. But does that introduce an incentive for all banks to behave the same way? No, it doesn’t. This is partly because many banks don’t care about market risk RWAs (think Wells Fargo or Lloyds) and partly because even the ones that do don’t base their behaviour simply on what is cheapest in capital terms.
In short, letting banks use their own models for market risk RWA calculation reduces investor trust without adding much if any robustness. Root them out, cut costs*, and set a standard that is believable and whose information content is easily understood.
*Which are enormous.