Generalized Lottery Trees: Budget-Balanced Incentive Tree Mechanisms for Crowdsourcing

Incentive mechanism design has aroused extensive attention for crowdsourcing applications in recent years. Most research assumes that participants are already in the system and aware of the existence of crowdsourcing tasks. Whereas in real-life scenarios without this assumption, it is more effective to leverage incentive tree mechanisms that incentivize both users' direct contributions and solicitations to other users. Although such mechanisms have been investigated, we are the first to propose budget-balanced incentive tree mechanisms, called generalized lottrees, which require the total payout to be equal to the announced budget, while guaranteeing several desirable properties including continuing contribution incentive, continuing solicitation incentive, value proportional to contribution, unprofitable solicitor bypassing, and unprofitable Sybil attack. Moreover, three types of generalized lottree mechanisms, 1-Pachira, K-Pachira and Sharing-Pachira, are presented for supporting diversified requirements. A solid theoretical guideline on the mechanism selection is provided based on the Cumulative Prospect Theory. Both extensive simulations and realistic experiments with 82 users are conducted to confirm our theoretical analysis.