Variation in experimental instructions: Punishment in public goods games

We provide evidence that more explicit, and hence longer, instructions can affect behaviour in a public goods game with punishment. Instructions that highlight the positive externality associated with public goods contributions, provide more examples, and emphasize fundamental aspects of the decision setting are associated with higher contribution levels in games with punishment opportunities when compared to shorter, less explicit instructions. These changes are not found to impact behaviour in the simpler contribution game without punishment.