Treat the “Reasonable Person,” Not as an Abstraction, but as an Average

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The core of most determinations of negligence is the question, “What would a reasonable person have done?” And, at least in theory, this “reasonable person” isn’t supposed to be an actual person whose deeds are recorded in the admissible evidence. Instead, based on the instructions, it is an idea. It is left to the jury to understand, unpack, and apply that idea. On the legal fiction of the “reasonable person,” legal theorists have debated whether it is a concept guided by rational economics (what is reasonable is what is justified based on costs versus benefits), or guided by empirical observation (what is reasonable is that which is practiced by a substantial portion of the population). A new series of studies (Jaeger, 2021) set out to answer that question by determining how potential jurors practically understand and apply the concept of the “reasonable person.”

Baylor Law School Professor Christopher Jaeger conducted four experiments focusing on how the standard is used in an experimental mock trial setting. Specifically, the studies contrasted the empirical view that reasonable behavior is average behavior with the economic view that reasonable behavior is behavior with more benefits than costs. The simple answer was that reasonability was more social than rational: “Participants consistently used information about how other people would have acted to decide whether conduct was reasonable.” In this post, I’ll provide a brief overview of the studies and some of the implications for juror behavior on negligence claims.

The Research 

The author used brief vignettes of hypothetical negligence cases in which the defendant failed to take a precaution, together with information about either the rationality or the popularity of that precaution. Some participants received an economic rationale for the reasonability of the precaution in the form of information on its benefits versus costs. Other participants received empirical information on how common the precaution was, with the representation that either 10 percent or 90 percent of public followed that precaution. In two additional studies, the author also included a range of behaviors (with 0, 10, 25, 50, or 90 percent following the precaution) in order to see if the determination focused on the average (the majority) or the aspirational (behavior of the most cautious, even when in a minority).

Findings and Implications 

“Reasonable Person” Is Based on (Perceived) Common Practice

The main finding was that the determinations are empirical, not economic. In other words, the proportion of the public perceived as following, not a strictly rational calculation, but a social one: The more common a practice is represented as being, the more likely it is that participants would see it as negligent to not follow that practice. The economics, on the other hand, did not determine the response.

Of course, litigators might respond that an actual jury is unlikely to hear exactly that kind of information, with the popularity of a practice being either unsupported by evidence or inadmissible. But in some ways, that information might still find its way into a jury’s thinking. For example, an expert may be able to talk about the normalcy of various practices. Or in voir dire, jurors might share their own practices, which can impart a strong sense of what is common. Even without additional information during trials, jurors are also likely to arrive with their own sense of whether given precautions are common or rare.

The More Common, the Better

The part of the study that compared the proportion of the public following a giving precaution (contrasting 0, 10, 25, 50, or 90 percent) found that there was a linear relationship:  The more common a practice is perceived to be, the more likely a failure to follow that practice can be a basis for negligence. Interestingly, this linear relationship is in contrast to the theorized idea that it might be a threshold issue. That is, instead of there being a “jump” in negligence at the point of there being a substantial minority (25 percent) or an average (50 percent), there was a straight line of more participation being better all the way to ninety percent. So parties in litigation will want to think about what parts of the message might pull that perceived proportion either up or down.

But Common Practice Is Not the Only Factor 

The perceived popularity of precautions did not explain all of the variance in negligence determinations, showing that other factors are also in play. Those who were told the behavior was practiced by 90 percent were more likely to find the defendant negligent than those who were told the behavior was practiced by only 10 percent. Still, a majority — 50.5 percent — found negligence even when precautions are atypical and practiced by only one in ten. Fully 42 percent found the defendant negligent even with both the empirical and economic information was on the lower end. This could simply reflect the tendency for jurors to align their negligence determinations with a desire to achieve a given result (i.e., There’s an injury, and finding negligence is the way to take care of it). Alternately, jurors could rely not just on the perceptions of what is empirically common, but also on idealized versions of what the jurors themselves would have done. Applying hindsight, it is easy for most to want to believe that they would have taken the precaution that could have avoided the injury.

Ultimately, it is a complex subject, but one worth thinking about and testing in the context of your own case. When jurors are asked to decide on the reasonability of a defendant’s actions, what implicit standard will they bring and apply?


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

Image credit:, used under license

DISCLAIMER: Because of the generality of this update, the information provided herein may not be applicable in all situations and should not be acted upon without specific legal advice based on particular situations.

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