Stability of cooperation under image scoring in group interactions

TL;DR

This paper investigates how cooperation in group interactions is affected by the type of information available, showing that even minimal image scoring can sustain cooperation outside ideal conditions.

Contribution

It provides a combined analytical and simulation analysis of the impact of group scoring versus image scoring on cooperation sustainability.

Findings

Pure group scoring fails to sustain cooperation.

Small degrees of image scoring can promote cooperation.

The effectiveness of image scoring depends on population size.

Abstract

Image scoring sustains cooperation in the repeated two-player prisoner's dilemma through indirect reciprocity, even though defection is the uniquely dominant selfish behaviour in the one-shot game. Many real-world dilemma situations, however, firstly, take place in groups and, secondly, lack the necessary transparency to inform subjects reliably of others' individual past actions. Instead, there is revelation of information regarding groups, which allows for `group scoring' but not for image scoring. Here, we study how sensitive the positive results related to image scoring are to information based on group scoring. We combine analytic results and computer simulations to specify the conditions for the emergence of cooperation. We show that under pure group scoring, that is, under the complete absence of image-scoring information, cooperation is unsustainable. Away from this extreme case, however, the necessary degree of image scoring relative to group scoring depends on the population size and is generally very small. We thus conclude that the positive results based on image scoring apply to a much broader range of informational settings that are relevant in the real world than previously assumed.