Overdetermined Causation Cases, Contribution and the Shapley Value

The overdetermined causation cases (duplicative causation, concurrent causes, etc.) challenge the consistency and relevance of the but for test in torts. A strict application of the but for criterion to these cases leads to paradoxes and solutions that violate common sense. This explains why a large amount of literature has been developed in philosophy and jurisprudence to provide more accurate causation criteria. This paper adds to this literature by considering over-determination cases from an economic and mathematical point of view.

Following Martin van Hees and Matthew Braham in their 2009 article Degrees of Causation, we consider over-determined cases through cooperative game theory and define “overdetermined causation games”. We characterize these games in terms of marginal contribution to the great coalition and we provide a typology of different overdetermined causation cases. Lastly, we apply to these games a traditional sharing rule developed in cooperative game theory, the Shapley value, to assess the “causal” contribution of each tortfeasor.