Emotional reactions, perceived impact and perceived responsibility mediate the identifiable victim effect, proportion dominance effect and in-group effect respectively

• Three psychological mechanisms were tested as mediators of three helping effects.
• The identifiable victim effect was primarily mediated by emotional reactions (especially sympathy).
• The proportion dominance effect was primarily mediated by perceived impact.
• The in-group effect was primarily mediated by perceived responsibility.

This study investigated possible mediators of the identifiable victim effect (IVE), the proportion dominance effect (PDE), and the in-group effect (IGE) in helping situations. In Studies 1–3, participants rated their emotional reactions (distress and sympathy toward the victims), perceived impact of helping, perceived responsibility to help, and helping motivation toward four versions of a helping situation. Gradually increasing victim identifiability in the helping situations primarily affected emotional reactions and sympathy completely mediated the IVE. Gradually making the reference-group smaller primarily affected perceived impact, and impact completely mediated the PDE. Gradually increasing in-groupness primarily affected perceived responsibility, and responsibility completely mediated the IGE. Study 4 included real monetary allocations and largely replicated the results using a between-subject design. Together, the results shed light on how contextual factors trigger help motivation, and indicate that different helping effects are primarily mediated by different mechanisms.