Abstract

Experimenter demand effects refer to behavioral changes that result from participants shifting their response in reaction to an inference on the experimenter’s hypothesis. These effects threaten both the internal and external validity of a study. This threat is taken seriously by experimental economists, who have developed a number of best practices to suppress or eliminate the potential role of such effects. We outline these best practices and review the literature to show that they are followed in the vast majority of published work. This adherence to best practice likely contributes to the limited evidence of such effects uncovered in the literature. Specifically, we are not aware of examples where demand effects have been shown to influence the qualitative inference from a study. While good design goes a long way towards reducing the potential for experimenter demand effects, a complementary option, presented in our final section, is to derive bounds on them.