Ces dernières années, la littérature autour des nudges pour améliorer la qualité environnementale a pris de l’ampleur avec la publication de nombreuses expériences de terrain et l’élaboration de modèles théoriques. En rapprochant la littérature empirique de celle autour des modélisations théoriques, nous discutons les principaux résultats, mais aussi les principales limites de ces approches. En particulier, si les premières études empiriques semblaient indiquer des résultats encourageants avec la mise en place des nudges, des études plus récentes montrent des résultats bien plus nuancés avec, pour certaines, une absence d’effet de ces instruments. En outre, les modèles théoriques actuels, bien qu’étant une première étape, ne permettent pas encore d’appréhender de manière fine la psychologie des agents visés par les nudges.

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This article presents a particular viewpoint on how nudge should be understood. The concept of nudge has generated considerable interest among academics and policymakers. However, ten years later, what is meant exactly by "nudge" is still a matter of debate. In fact, there is a fundamental discrepancy between the (original) narrow definition of Thaler and Sunstein (nudge in the narrow sense, NN) and the (later) broad definition of Sunstein (nudge in the broad sense, NB). These two definitions differ regarding the instrumental use of rationality failures, and accordingly whether the provision or disclosure of information counts as a nudge or not. From a pragmatic perspective, the paper argues for a position that consists of adopting the broad definition of a nudge while acknowledging several types of nudges, which we provide in an integrative view. We suggest that future research should assess the effectiveness of these different types of nudges separately.

We provide an experimental test of the theoretical predictions obtained in Ouvrard and Spaeter (2016). A public goods experiment is proposed in which the subjects can contribute to reduce the level of pollution, which is stochastic. A nudge (announcement of the socially optimal contribution) and a tax are implemented to improve the level of contributions. The environmental sensitivity and optimism of the subjects are also elicited. Our first result shows that the implementation of the nudge does not perform as well as the implementation of the tax. The reaction to the nudge depends directly on individuals' environmental sensitivity, contrary to the reaction to the tax. Secondly, the nudge performs well with highly sensitive subjects only during the first half of its implementation. Lastly, the e ciency analysis shows that the implementation of the nudge significantly decreases the groups' welfare for the least sensitive subjects, in comparison to the baseline. In sum, these results tend to corroborate the predictions obtained in Ouvrard and Spaeter (2016).

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