On the Relevance of Irrelevant Strategies

We experimentally examine whether adding seemingly irrelevant strategies, such as a dominated strategy or a duplicate of an existing strategy, affects players’ behavior in simultaneous games. In coordination games, we find that adding a dominated strategy increases the likelihood that players choose the strategy which dominates it, and duplicating a strategy increases its choice share; The players’ opponents seem to internalize this behavior and best respond to it. In single-equilibrium games, these effects disappear. Consequently, we suggest that irrelevant strategies affect behavior only when they serve a strategic purpose. We describe an adapted level-k model that explains our findings