A randomised field experiment was designed and conducted during an election in newly oil-rich Sao Tome and Principe to infer effects of vote-buying on electoral behaviour.

Vote-buying, i.e., cash-for-votes, is a frequent practice during election time in many parts of the world, namely in West Africa. However, in the presence of secret ballots, it is not clear whether and how vote-buying drives voting behaviour. In order to infer effects of vote-buying on electoral behaviour, we designed and conducted a randomised field experiment during an election in newly oil-rich Sao Tome and Principe. We follow a randomized voter education campaign against vote-buying sponsored by the Electoral Commission, using panel-survey measurements as well as actual electoral data per ballot station. Our experimental results show that the campaign reduced the influence of money offered on voting, decreased electoral participation, and favoured the incumbent. This evidence suggests that vote-buying increases voter turnout and that the challenger drives relatively more votes through vote-buying - i.e., that vote-buying counteracts the incumbency advantage.