Résumé
We examine experimentally how and why voluntary contributions are affected by sequentiality. Instead of deciding simultaneously in each round, subjects are randomly ordered in a sequence which differs from round to round. We compare sessions in which subjects observe the contributions from earlier decisions in each round (“sequential treatment with information”) to sessions in which subjects decide sequentially within rounds, but cannot observe earlier contributions (“sequential treatment without information”). We also investigate whether average contributions are affected by the length of the sequence by varying group size. Our results show that sequentiality alone has no effect on contributions, but that the level of contributions increases when subjects are informed about the contributions of lower-ranked subjects. We provide evidence that the so-called “leadership effect” vanishes within rounds, and that group size has no significant impact on the average level of contributions in our sequential contribution games.