Contracting with a Mechanism Designer

Abstract: This paper explores the economic interactions within modern crowdsourcing markets. In these markets, employers issue requests for tasks, platforms facilitate the recruitment of crowd workers, and workers complete tasks for monetary rewards. Recognizing that these roles serve distinct functions within the ecosystem, we introduce a three-party model that distinguishes among the principal (the requester), the intermediary (the platform), and the pool of agents (the workers). The principal, unable to directly engage with agents, relies on the intermediary to recruit and incentivize them. This interaction unfolds in two stages: first, the principal designs a profit-sharing contract with the intermediary; second, the intermediary implements a mechanism to select an agent to complete the delegated task. We analyze the proposed model as an extensive-form Stackelberg game. Our contributions are fourfold: (1) We fully characterize the subgame perfect equilibrium. In particular, we reduce the principal's contract design problem to a novel auction-theoretic formulation we term virtual value pricing, and reveals that linear contracts are optimal even when the task have multiple outcomes and agents' cost distributions are asymmetric. (2) To quantify the principal's utility loss from delegation and information asymmetry, we introduce the price of double marginalization (PoDM) and the classical price of anarchy (PoA), and derive tight or nearly tight bounds on both ratios under regular and monotone hazard rate (MHR) distributions. (3) We further examine these two ratios in a natural setting where the intermediary is restricted to anonymous pricing mechanisms, and show that similar qualitative insights continue to hold. (4) Finally, we extend our results on both ratios to a robust framework that accommodates scenarios in which the principal lacks precise information about the market size.