سهل انگاری تطبیقی در برابر سهل انگاری موثر: مقایسه هزینه های شکایت های قانونی

The previous literature on comparative and contributory negligence points out that administrative costs are higher under comparative negligence because the courts must decide on the degree of negligence by both parties and not just whether the parties were negligent. In this article, I show that this finding is not necessarily correct. I use a rent seeking model to show that the litigation expenditures may be smaller under comparative negligence. The previous literature has focused on only one effect, while there may be three effects at play.

In the United States as well as in Europe, comparative negligence rather than contributory negligence is the general rule in tort law (see Artigot i Golobardes & Gómez Pomar, 2009).1 Comparative negligence divides the cost of harm between the parties in proportion to the contribution of their negligence to the accident. Under a rule of (negligence with a defense of) contributory negligence, the negligent injurer can escape liability by proving that the victim's precaution fell short of the legal standard of care (see Cooter & Ulen, 2003). Although these negligence rules have been examined quite extensively in the law and economics literature, it is still debated whether comparative negligence creates better incentives for parties to adopt efficient care than contributory negligence (see e.g. Artigot i Golobardes and Gómez Pomar, 2009 and Bar-Gill and Ben-Shahar, 2003). The early literature concluded that contributory negligence is more efficient (e.g. Brown, 1973, Diamond, 1974 and Posner, 1977).2 Later it was shown that both rules are equivalent from an efficiency perspective when information is perfect and decision-makers are error-free (e.g. Haddock and Curran, 1985 and Shavell, 1987)3, but that the equivalence does not hold when these assumptions are relaxed (e.g. Cooter and Ulen, 1986 and Haddock and Curran, 1985).4 At first, relaxing the assumptions seemed to favor comparative negligence, but more recent literature is rather sceptical concerning any general superiority of one of these liability regimes (e.g. Bar-Gill & Ben-Shahar, 2003).5,6 This ongoing debate stands in contrast to the lack of conflicting opinions with respect to the relative size of the administrative costs under both negligence rules. Comparative negligence is generally considered to generate higher costs per case. Landes and Posner (1987) observe that comparative negligence costs more to administer than contributory negligence. Shavell (1987) states that the defense of contributory negligence may lead to less complicated proceedings compared to comparative negligence. White (1989) argues that comparative negligence seems to generate higher litigation and administrative costs than the traditional negligence rules because the courts must decide on the degree of negligence by both parties and not just whether the parties were negligent. Bar-Gill and Ben-Shahar (2001) state that contributory negligence might be cheaper to administer than comparative negligence.7 The point of view that comparative negligence entails higher costs per case is obviously true in a setting with exogenous litigation costs. The additional element of weighing the parties’ degree of negligence indeed generates extra costs. However, the previous literature has overlooked the fact that different effects (more precisely, three) are at play in a more realistic setting in which litigation costs are endogenous.8 We show that in such a setting, comparative negligence can be less costly than contributory negligence. The kernel of the argument can be explained with a simple numerical example. Suppose (for simplicity) that the defendant's negligence is certain and that the parties share the loss (J) equally when also the plaintiff is held liable. The plaintiff can make an additional investment 9 to increase his chances of not being held liable from 20% to 50%. 10 Under a rule of contributory negligence, the marginal benefit from this extra investment equals 0.5.J − 0.2.J = 0.3.J. Under a rule of comparative negligence, the marginal benefit of the extra investment is smaller: (0.5.J + 0.5.J/2) − (0.2.J + 0.8.J/2) = 0.15.J. Clearly, the benefit is smaller under a rule of comparative negligence. Intuitively, the stakes are higher under contributory negligence: if the plaintiff is held liable, he pays everything. Under comparative negligence, he only bears half of the harm. While the expenditures of the parties concerning the liability of the plaintiff are larger under contributory negligence, we can easily show that the expenditures concerning the liability of the defendant are larger under comparative negligence. Another numerical example can easily demonstrate this. Suppose that this time the plaintiff's negligence is certain and that once again the parties share the loss equally when also the defendant is held liable. The plaintiff can make an extra investment to increase the probability that the defendant will be held liable from 20% to 50%. Under a rule of contributory negligence, the marginal benefit from this extra investment equals 0 (since the plaintiff will bear the full loss, no matter whether the defendant is found negligent or not). Under a rule of comparative negligence, the marginal benefit of the extra investment is larger: 0.3.J/2. Intuitively, when it comes to the negligence of the defendant, the stakes are higher under comparative negligence. Note that things are more complex than this. Under comparative negligence the expenditures may also influence the court's perception of the degree of negligence and this may determine the division of the loss under this negligence rule. We incorporate this in the general model. We find a relatively simple condition for the case in which the total expenditures are smaller under comparative negligence than under contributory negligence. We will see that especially for high-quality claims, comparative negligence may lead to lower litigation costs than contributory negligence. 11 I stress that this article deals with one particular aspect of the relative efficiency of contributory and comparative negligence, namely their relative costs at trial. It does not address the overall efficiency of the two negligence standards. 12 We will proceed as follows. The following section provides a general model which incorporates contributory negligence and comparative negligence.13 Section 3 compares the litigation expenditures for contributory and comparative negligence. Section 4 concludes.

Litigation expenditures can be either smaller or larger under a rule of comparative negligence than under a rule of contributory negligence. The differences between both rules can be summarized as follows. First, comparative negligence increases the expenditures of the parties because the expenditures may influence the court's view on the relative degree of negligence, which only matters under comparative negligence. Second, comparative negligence also increases the expenditures regarding the defendant's negligence for another reason. The value of these expenditures is lower under contributory negligence, since these are worthless if the plaintiff is also held negligent. Third, comparative negligence can decrease the expenditures regarding the plaintiff's negligence. If the plaintiff is held liable under contributory negligence, he pays everything. Under comparative negligence, he only bears part of the harm. It thus becomes less worthwhile to fight hard. Total expenditures are more likely to be smaller under comparative negligence as the defendant's degree of fault increases relative to the plaintiff's degree of fault. Several extensions are possible. For example, instead of looking for the Nash equilibrium, we could look for the Stackelberg equilibrium. Indeed, the parties do not necessarily always choose their strategies simultaneously. In some instances, one side may be able to commit to a level of effort, to which the other side then makes an optimizing response. It would be natural to assume that it is the plaintiff who makes a commitment, since there is no lawsuit unless the plaintiff initiates it.31 Another extension could examine the expenditures regarding the defendant's and the plaintiff's negligence in a sequential trial.32 This article assumed trials are unitary. Finally, even in unitary trials, one could introduce the possibility that one party acknowledges his negligence or acknowledges that the other party did not act negligently, so that only one issue needs to be litigated. One could then analyze under which negligence rule the parties are more likely to do this.