Presumption of Negligence and the Robustness of Liability Incentives

In negligence regimes, tort plaintiffs traditionally bear the burden of proving the negligence of their defendants. Several European legal systems adopted rules that have reversed this traditional evidentiary rule in certain categories of torts, creating a rebuttable presumption of negligence against defendants. Under this presumption, the tortfeasor faces the burden of proving to have met the standard of due care to rebut the legally created presumption of negligence. This paper analyzes the conditions under which it might be optimal to shift evidentiary burdens, creating a presumption of negligence which the defendant must affirmatively rebut. We analyze the effects of legal presumptions on care and activity levels incentives. Our analysis reveals that a change in presumptions can increase the robustness of care incentives in the face of probatory difficulties and operates as an activity-level tax which can mitigate the activity level of the party who is not already burdened by residual liability. We suggest that the interaction between evidence and substantive tort rules is an important dimension that should inform the choice of legal presumptions