Sunday, June 23, 2013

Models aren't Optional

Models get a bad break, and the key is remembering the golden mean: moderation in all things. Macroeconomics, String Theory, Climate studies, all produce highly complicated models that are presented by our best academics as being thoroughly vetted and informative. Yet, for predictions in the real world, they stink. This leads to people saying models are all garbage, and we should all be engineers. Clearly a bad model is worse than no model, but if you are operating in some domain, you have implicitly or explicitly, a model of that domain. in this way, it's simply nice to write it down as clearly as possible to better understand what you are doing.

 I came across the The Good Regulator theorem (1970) by Roger Conant and Ross Ashby. It is stated "Every Good Regulator of a system must be a model of that system".
the theorem shows that, in a very wide class (specified in the proof of the theorem), success in regulation implies that a sufficiently similar model must have been built, whether it was done explicitly, or simply developed as the regulator was improved. Thus the would-be model-maker now has a rigorous theorem to justify his work.
I don't really follow the proof, but I think it's definitely true that to regulate something well, you need a good model of that something. 


Min said...

The Flathead Indians used cradleboards to fashion the shape of their children's foreheads. That is effective regulation. Where is the necessary model?

Eric Falkenstein said...

Good one. I bet they thought this was perversely helpful, in the same way that those Africans who create elongated necks by pushing down their clavicles, or Chinese who created deformed feet, thought this emulated the 'perfect type' better, and via some Lamarckian mechanism, was helpful. It's a bad theory/model, but it's there.

Min said...

Chines foot binding is a great example. :) IIUC, the smellier the tiny feet were, the better.

Min said...

I actually had a point with my example, which is that the question of good systemic regulation has an empirical aspect. Simply observing the growth of the skeleton is unlikely to tell you the result of binding or cradle boards. One might surmise, from general considerations, that the body would adapt to those constraints rather than bursting through them or breaking, but the proof is in the pudding. Without seeing the results of these attempts at regulation, it would be difficult to arrive at a good model of skeletal growth.

rs gold said...

My partner and i bet they believed this was perversely useful, just like that those Africans that generate pointed necks through driving along their own clavicles, or even Oriental that created misshaped feet, thought this particular copied the 'perfect type' greater, and also by means of a number of Lamarckian device, had been useful. It's a undesirable theory/model, but it's generally there.

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