Spatio‐temporal risk sharing and transfer: A unified theory of multi‐period decentralized insurances and annuities

Abstract Two distinct strands of research focus on decentralized risk sharing plans. One strand centers on classic risk sharing and decentralized insurance, including peer‐to‐peer insurance, mutual aid, and DeFi insurance. The other explores decentralized annuities, such as tontine and group self‐annuitization. Despite their disparate development paths, both involve decentralized risk sharing and transfer among participants. This paper aims to unify these domains by extending a theory of decentralized insurance to encompass multi‐period decentralized insurances and decentralized annuities. The framework illuminates connections between spatial risk sharing and intertemporal risk transfer, and enables economic analysis of diverse scheme designs. The paper also provides a comprehensive review of various notions of temporal and spatial actuarial fairness, elucidating how different designs emerge from these distinct notions.