Le thermostat de Milton Friedman

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Incognito
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Le thermostat de Milton Friedman

Message non lu par Incognito » 24 févr. 2013, 11:33:01

Suite au commentaire suivant, http://actu-politique.info/post246889.html#p246889, je me suis dis que ce serait une bonne idée de rappeler le concept du thermostat de Milton Friedman.

Le concept du thermostat expliqué par un économiste canadien:
http://worthwhile.typepad.com/worthwhil ... ostat.html
Everybody knows that if you press down on the gas pedal the car goes faster, other things equal, right? And everybody knows that if a car is going uphill the car goes slower, other things equal, right?

But suppose you were someone who didn't know those two things. And you were a passenger in a car watching the driver trying to keep a constant speed on a hilly road. You would see the gas pedal going up and down. You would see the car going downhill and uphill. But if the driver were skilled, and the car powerful enough, you would see the speed stay constant.

So, if you were simply looking at this particular "data generating process", you could easily conclude: "Look! The position of the gas pedal has no effect on the speed!"; and "Look! Whether the car is going uphill or downhill has no effect on the speed!"; and "All you guys who think that gas pedals and hills affect speed are wrong!"

And no, you can not get around this problem by doing a multivariate regression of speed on gas pedal and hill. That's because gas pedal and hill will be perfectly colinear. And no, you do not get around this problem simply by observing an unskilled driver who is unable to keep the speed perfectly constant. That's because what you are really estimating is the driver's forecast errors of the relationship between speed gas and hill, and not the true structural relationship between speed gas and hill. And it really bugs me that people who know a lot more econometrics than I do think that you can get around the problem this way, when you can't. And it bugs me even more that econometricians spend their time doing loads of really fancy stuff that I can't understand when so many of them don't seem to understand Milton Friedman's thermostat. Which they really need to understand.
Ce concept me paraît particulièrement important quand on parle de l'effet d'un stimulus monétaire ou budgétaire sur l'économie.
Dieu est mort. Marx est mort. Et moi-même je ne me sens pas très bien ... (Woody Allen)

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El Fredo
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Re: Le thermostat de Milton Friedman

Message non lu par El Fredo » 24 févr. 2013, 12:09:33

Bien vu, je ne connaissais pas.
If the radiance of a thousand suns were to burst into the sky, that would be like the splendor of the Mighty One— I am become Death, the shatterer of Worlds.

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Golgoth
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Re: Le thermostat de Milton Friedman

Message non lu par Golgoth » 24 févr. 2013, 22:01:03

En fait en ce moment on lache plutôt l'accélérateur dans une montée, non ?
T'es vraiment kon François, fallait créer une SCI. :mrgreen2:

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El Fredo
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Re: Le thermostat de Milton Friedman

Message non lu par El Fredo » 24 févr. 2013, 22:47:39

On a déjà passé la marche arrière.
If the radiance of a thousand suns were to burst into the sky, that would be like the splendor of the Mighty One— I am become Death, the shatterer of Worlds.

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