A classic finding is the strength-is-weakness effect; that weaker players often bond together and that the strong party is relatively more often excluded from a coalition than one would expect. The original studies on this were conducted with relatively low sample sizes, so we wanted to explore how robust the effect was (before looking at processes).
We've developed an open-source tool in O-tree to conduct behavioral experiments with 3party coalitions (the Online Coalition game). This can be integrated with Prolific or mTurk to allow coalition formation in studies with 100s of participants in triadic negotiatons.
The PSPB paper replicates the effect, and finds that it largely exists because the strong players overclaim (ask for a reward based on equity), while the weak players want to be somewhere in between equality and equity. The 2021 EJSP elaborates on this and finds that players seem to actively prefer equality or equity as the fair norm, depending on what is in their own best interest. Finally, the 2023 EJSP finds that the more deserved the advantage of the stronger party is, the less likely they are to be excluded from the coalition.