On the behavioural relevance of optional and mandatory impure public goods

Impure public goods combine a private good with a public good. Often, impure public goods have a charitable or ethical dimension, giving ethically motivated consumers a convenient option to contribute to public goods through the marketplace (in addition to direct donations). Impure public goods could potentially promote ethical giving or alternatively hinder charitable behaviour. We implement an economics experiment with a between-subject design to test the behavioural relevance of impure public goods with only a token (i.e. small) contribution to a public good. Contributions to the public good are negatively affected by the presence of impure public goods with token contributions. We explore one mechanism to offset this negative impact by making the token impure public good mandatory. We observe higher average contributions and several positive impacts on charitable behaviour, which supports the claim that this mechanism can potentially offset the negative impact of impure public goods.