Bank UK John Keeble/Getty Images

Le déni des économistes

LONDRES – Au début du mois dernier, Andy Haldane, économiste en chef à la Banque d'Angleterre, a expliqué que l’échec des modèles de prévision récents de la BoE est dû au « comportement irrationnel » des agents économiques. Le fait de ne pas avoir repéré cette irrationalité avait amené les décideurs à prévoir que l'économie britannique ralentirait dans le sillage du référendum sur le Brexit en juin dernier. Au lieu de cela, les consommateurs britanniques se sont lancés dans une frénésie de dépenses inconsidérées depuis la décision de quitter l'Union européenne; et, de manière tout aussi illogique, les secteurs de la construction, des produits manufacturés et des services ont rebondi.

Haldane ne donne aucune explication pour cette explosion de comportement irrationnel. Il ne le peut pas, d’ailleurs: pour lui, l'irrationalité signifie simplement un comportement qui est incompatible avec les prévisions dérivées du modèle de la BoE.

Il ne s’agit pas seulement de Haldane ou de la BoE. Ce que les économistes traditionnels entendent par comportement rationnel n’est pas ce que vous et moi avons en tête. Dans le langage ordinaire, un comportement rationnel est un comportement raisonnable étant donné les circonstances. Or, dans le monde raréfié des modèles de prévision néoclassiques, cela signifie que les gens, grâce à une connaissance détaillée d'eux-mêmes, de leur environnement et de l'avenir face à eux, agissent de façon optimale pour atteindre leurs objectifs. En d’autres termes, agir de façon rationnelle est agir d'une manière compatible avec les modèles de comportement rationnel des économistes. Face à un comportement contraire, l'économiste réagit comme le tailleur qui blâme le client de ne pas être adapté au costume qu’il vient de réaliser.

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