In oligopoly, imitating the most successful competitor yields very competitive outcomes. This theoretical prediction has been confirmed experimentally by a number of studies. A recent paper by Friedman et al. (J Econ Theory 155:185-205, 2015) qualifies those results in an interesting way: While they replicate the very competitive results for the first 25-50 periods, they show that when using a much longer time horizon of 1200 periods, results slowly turn to more and more collusive outcomes. We replicate their result for duopolies. However, with 4 firms, none of our oligopolies becomes permanently collusive. Instead, the average quantity always stays above the Cournot-Nash equilibrium quantity. Thus, it seems that ''four remain many'' even with 1200 periods. Keywords Imitation Á Experiment Á Cournot oligopoly Á Walrasian outcome JEL Classification C91 Á C72 Á D74 Electronic supplementary material The online version of this article (

We implement an experiment to elicit subjects' ambiguity attitudes in the spirit of Ellsberg's three-color urn. The procedure includes three design elements that (together) have not been featured in similar experiments: Strict ambiguity preferences, a single decision, and a mechanical randomization device with an unknown distribution (to both subjects and experimenters). We use this device in order to eliminate possible 'strategic' ambiguity related to subjects' beliefs about the experimenters' motivations. In addition, we survey 40 experimental studies on Ellsberg's two-and three-color problems, and find that, on average, slightly more than half of subjects are classified as ambiguity averse. Our results, with our new design, fall on the low end of the range of results in the surveyed studies, and are comparable to a control test where "strategic" ambiguity was induced.

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