Sharps, D.+, & Schroeder, J. (2019). The preference for distributed helping. Journal of Personality and Social Psychology, 117, 954-977.
This paper investigates the psychology underlying how people decide to allocate help (e.g., donations) among multiple needy requesters, and documents a preference for distribution (allocating help to multiple requesters) compared to concentration (allocating help to a single requester) (9 experiments).