Dateline: October, 2021, Issue 3

How do jurors determine what a reasonable person would do?

Tort liability often hinges on whether a defendant behaved as a "reasonable person" would have under the circumstances. Jurors often must decide if a defendant acted as would a reasonably prudent person or as would reasonable people exercising ordinary care.

Jaeger (2021) conducted four experiments exploring how potential jurors conceive of the "reasonable person." The first two experiments tested whether mock jurors interpret the reasonable person standard in empirical terms (based on what others do) or economic terms (based on cost efficiency). The third and fourth experiments examined how laypeople apply the empirical standard.

In the first two experiments, mock jurors decided 4 hypothetical negligence cases. Each case involved an injured plaintiff suing a defendant for failing to take a particular precaution that would have prevented the plaintiff's injury. Each case also contained two additional bits of information: (1) either that 10% or that 90% of those in the defendant's position would have chosen to take the relevant precaution, and (2) either that the precaution was cost-justified or that it was not cost-justified. Mock jurors rendered a verdict for each of the 4 provided cases.

In these two experiments, negligence decisions consistently depended on information about the behavior of others and never depended on whether the precautions were cost-justified. As might be expected, defendants were judged negligent more often when 90% of similarly situated others would have taken the precaution than when 10% would have done so. Economic information did not influence negligence verdicts, even when only 10% of similarly situated others would have taken the precaution. Further, a substantial share of mock jurors (42%) found the defendant negligent when both empirical and economic information suggested the defendant was not negligent, that is, when the defendant's conduct was both customary and economically justified, underscoring that considerations beyond custom and cost-justification influenced mock jurors' verdicts.

Experiments 3 and 4 explored if jurors understand the empirical reasonable person as "averageness" or "aspirational":

In this second set of experiments, mock jurors decided five negligence cases. No economic information about the cost of a precaution was provided in the case vignettes. The case vignettes included empirical information, with each vignette stating that either 0%, 10%, 25%, 50% or 90% of others in the defendant's position would have taken the precaution the defendant failed to take. Using a pure aspirational understanding, mock jurors would not find defendants negligent when 0% of others would take the precaution, but would find them negligent over some low threshold (10% or 25%). Using a pure averageness understanding, mock jurors would not find defendants negligent until a 50% threshold was reached on the empirical information continuum.

Empirical information again significantly affected mock jurors' negligence determinations. The more that others in the defendant's position would have taken a precaution, the more mock jurors judged a defendant negligent. This relationship between the percentage of others who would have taken a precaution and judged negligence appears linear, and is inconsistent with the "threshold jumps" predicted by both the averageness (50% threshold) and aspirational (10% or 25% threshold) understandings of the empirical reasonable person. Additionally, while empirical information about others' behavior influenced jurors' negligence judgments, it did not dictate those judgments completely, underscoring again that considerations beyond what others would have done influenced mock jurors' verdicts.

Jaeger concludes that laypeople understand reasonableness more in behavioral than in economic terms, and may not understand reasonableness in economic terms at all. Laypeople consistently use information about how other people would have acted to decide whether conduct was reasonable, although this only partly explains jurors' negligence determinations.

Source Jaeger, C.B. (2021). The empirical reasonable person. Alabama Law Review, 72(2), pp.887-957.