AUTHOR COPY Original Article Internal and External Validity in Experimental Games: A Social Reality Check Cecile Jackson University of East Anglia, Norwich, UK. Abstract The relevance of experimental games as methods in development research depends crucially on how far the results from the games can be extrapolated to real life, that is, the external validity of those results. The extent to which external validity matters depends on what you want to do with the data; some kinds of theory testing can arguably afford indifference, but many experi- ments are used as an indicator of behaviour in everyday life. This article takes an anthropological perspective on both the internal and external validity of social preference experiments in developing country settings, and argues for more cautious knowledge claims, triangulation of data and a broader conceptualisation of norms and behaviour. La pertinence des jeux expe´rimentaux en tant que me´thodes dans la recherche sur le de´veloppement de´pend fondamentalement de la mesure dans laquelle les re´sultats obtenus a` partir de ces jeux s’appliquent a` la re´alite´, c’est a` dire de la validite´ externe de ces re´sultats. La validite´ externe est plus ou moins importante selon ce que l’on souhaite faire avec les donne´es. Certains types de jeux testent des the´ories sans se soucier de leur validite´ externe, mais d’autres sont tenus comme e´tant des indicateurs de comportements quotidiens. Cet article examine a` partir d’une perspective anthropologique les validite´s tant internes qu’externes d’expe´riences de pre´fe´rences sociales dans un contexte de pays en de´veloppement, et plaide en faveur de revendications the´oriques plus prudentes, de triangulations de donne´es, et d’une conceptualisation plus large des normes et des comportements. European Journal of Development Research advance online publication, 15 December 2011; doi:10.1057/ejdr.2011.47 Keywords: experimental economics; interdisciplinary; cross-cultural; social preferences; games Introduction Testing theory against real-life behaviour in controlled experimental conditions has become an important approach in economics, inspired by scepticism about the fit between assump- tions and real-life behaviour. It is therefore ironic that it is concern about the external validity of experimental evidence, that is, the degree to which it can be extrapolated to explain social reality outside of the experimental context, which is perhaps the greatest blockage to wider interdisciplinary engagement with this field. This article focuses on this question in order to clarify the nature of the problem from a social anthropological pers- pective, and to indicate what caveats are appropriate to knowledge claims from expe- rimental evidence, how limitations may be addressed, and what requires better theorisation in this field (Swedberg, 2001). For interdisciplinary development research, an engagement by anthropologists with these experimental methods of economics looks promising. The experimental turn in r 2011 European Association of Development Research and Training Institutes 0957-8811 European Journal of Development Research 1–18 www.palgrave-journals.com/ejdr/