Rational expectations — only for Gods and idiots

In a laboratory experiment run by James Andreoni and Tymofiy Mylovanov — presented here — the researchers induced common probability priors, and then told all participants of the actions taken by the others. Their findings is very interesting, and says something rather profound on the value of the rational expectations hypothesis in standard neoclassical economic models: We look at choices in round 1, when individuals should still maintain common priors, being indifferent about the true state. Nonetheless, we see that about 20% of the sample erroneously disagrees and favors one point of view. Moreover, while other errors tend to diminish as the experiment progresses, the fraction making this type of error is nearly constant. One may interpret disagreement in this case as evidence of erroneous or nonrational choices. ….[READ]