Trust Masters, Not Models

Normally, when I write about markets, I try to point at models but there is a lot of guesswork and gut-work in analysis. When times are sort of normal, then models can be a big part of what drives your thinking. But times have not been ‘normal’ for a very long time, and this is part of what drives big policy errors (and big forecasting errors): if you are out of the ‘normal’ range, then to make a forecast or comment usefully on what is going on you need to have a good feel for what the model is actually trying to capture. You need to know where the model goes wrong.

When I was a rates options trader – stop me if I’ve told this story before – I found that I preferred to use a simple Black-Scholes pricing model instead of some fancy recombining-trinomial-tree-with-heteroskedastic-volatility-model. That was because even though Black Scholes doesn’t match up super well with reality, I at least had a good feel for where it fell short. For example, the whole reason we have a volatility smile is because real-world returns have fat tails, but pricing models like Black Scholes are based on the normal distribution. When the smile flattens, it means returns are becoming more like they’re being drawn from a normal distribution; when it steepens it means that the tails are becoming fatter. So that’s easy to understand.

If you understand why an option model works, then it’s easier to think about how to price something esoteric like an option on an inflation swap (which can trade at a negative rate, but actually isn’t a rates product at all but rather is a way of trading a forward price), and not mess it up. But if you just apply and try to calibrate a bad model – especially if it’s really complicated – then you get potentially really bad outcomes. And that is, of course, exactly where we are today.

We haven’t been ‘normal’, I guess, for a couple of decades. Central banks, and in particular the Federal Reserve, have dealt in the markets with a heavier and heavier hand. Nowadays, the Fed not only has expanded its balance sheet by trillions in a very short period of time, but it has expanded the range of markets it is involved in from Treasuries to mortgages to ETFs and now individual corporate bonds. And, since the whole point of this is because the Fed wants to make sure the stock market stays elevated (they are preternaturally terrified at the notion of a wealth effect from a market crash, even though historically the wealth effect has been surprisingly small) I suspect it is only a matter of time before they directly intervene in equity markets.[1] C’est la vie. There is no normal any more.

But at least the ‘normal’ we have had over the last decade was just modestly outside of the prior normal. Things didn’t work right according to the ‘traditional’ way of thinking about things; momentum became ascendant in a way we’ve never seen before and value almost irrelevant. We are now, though, working on a whole different part of the number line. This means that economists will continue to be surprised at almost everything they see, and it means that any model you look at needs to be informed by a good intuition about how the hell it works.

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