Voluntary contributions of time: Time-based incentives in a linear public goods game

This paper presents the findings of an experimental study designed to investigate whether the pattern of contributions elicited in a Voluntary Contribution Mechanism (VCM) replicates the stylized facts reported in the literature when participants' time, rather than their money, is at stake. In this experiment, participants are all confronted to the same incentive structure. For half of them, the game is materialized using monetary payoffs, as is done in standard VCM studies. For the other half, the returns from the private and public accounts are implemented as reductions in waiting time. Experimental procedures are designed to keep the decision domain, the size of incentives and the degree of confidentiality constant across the two resources. The contribution patterns elicited by both treatments are found to be (i) remarkably similar and (ii) in line with the picture typically drawn in the literature. Group contributions are statistically indistinguishable in terms of average, variability and distribution, in virtually all rounds of the game. Although I do find a significant difference in the decay rate of contributions across rounds, seemingly driven by a greater proportion of early free-riders and late full contributors in the Time Treatment, this effect is both small in magnitude and inconsequential in terms of game efficiency. Overall, the stylized facts often presented in the VCM literature seem to be robust to a change in operationalization of the incentive structure.