Multiple causation, apportionment and the Shapley value

Multiple causation is one of the most intricate issues in contemporary tort law. Sharing a loss suffered by a victim among multiple tortfeasors is indeed difficult and Courts do not always follow clear and consistent principles. Here, we argue that the axiomatic approach provided by the theory of cooperative games can be used to clarify that issue. We have considered the question from a purely game theoretic point of view in Dehez and Ferey (2013). Here we propose to analyze it in a legal perspective. We consider in particular the difficult case of successive causation to which we associate a general class of games called "sequential liability games". We show that our model rationalizes the two-step process proposed by the Restatement Third of Torts, apportionment by causation and apportionment by responsibility. More precisely, we show that the weighted Shapley value associated to a sequential liability game is the legal counterpart of this two-step process.