Effect of direct reciprocity on continuing prosperity of social networking services

This paper investigates the effect of direct reciprocity on voluntary participation in social networking services (SNS) by modeling them as a type of public goods (PG) game. Because the fundamental structure of SNS is similar to the PG games, some studies have focused on why voluntary activities in SNS emerge by modifying the PG game. However, their models do not include direct reciprocity between users, even though it is known that reciprocity is a key mechanism to maintain and evolve cooperation in human society — one that is actually observed on SNS. To analyze the effect of reciprocity on SNS, we first developed an abstract model of SNS called reciprocal rewards and meta-rewards games that are extensions of the PG game. Then, we conducted experiments to understand how reciprocity facilitates cooperation by examining the proposed games using complete-graphs, WS networks, and a Facebook network. Finally, we analyze the findings derived from our experiments using the reciprocal rewards games and propose the concept of half free-riders to explain what maintains cooperation-dominant situations.