Res Ipsa Loquitur: Reducing Confusion or Creating Bias?

62 Pages Posted: 31 Mar 2020 Last revised: 21 Aug 2020

See all articles by Jeffrey H. Kahn

Jeffrey H. Kahn

Harry M. Walborsky Professor, Florida State University College of Law; Associate Dean, Business Program

John E. Lopatka

The Pennsylvania State University (University Park) – Penn State Law

Date Written: March 6, 2020

Abstract

The so-called doctrine of res ipsa loquitur has been a mystery since its birth more than a century ago. This Article helps solve the mystery. In practical effect, res ipsa loquitur, though usually thought of as a tort doctrine, functions as a rule of trial practice that allows jurors to rely upon circumstantial evidence surrounding an accident to find the defendant liable. Standard jury instructions in negligence cases, however, inform jurors that they are permitted to rely upon circumstantial evidence in reaching a verdict. Why, then, is another, more specific circumstantial evidence charge necessary or desirable?

We describe and evaluate the arguments that have been made in support of and in opposition to the res ipsa instruction. One theory is that jurors are confused in performing their task when given only standard instructions; the charge, therefore, clarifies their task, thereby improving the quality of their decisionmaking. A competing theory is that the instruction biases jurors in favor of plaintiffs, thereby degrading the quality of decisionmaking. Our theoretical analysis concludes that the bias explanation is stronger. We reach this conclusion by applying for the first-time modern learning on cognition to the res ipsa instruction.

To support our theoretical conclusion, we report the results of experiments designed to determine the effects of the instruction. All these experiments were intended first to confirm that the res ipsa instruction has an effect and second to confirm or refute our theoretical conclusion that the instruction biases rather than clarifies. While the empirical results did not demonstrate bias, they also failed to show the absence of bias. Moreover, we found no evidence that the instruction reduces confusion. Our conclusion is that the charge has no positive effect, and either may create a bias or, at best, is meaningless.

Suggested Citation

Kahn, Jeffrey H. and Lopatka, John E., Res Ipsa Loquitur: Reducing Confusion or Creating Bias? (March 6, 2020). Kentucky Law Journal, Vol. 108, 2020, Penn State Law Research Paper No. 09-2020, FSU College of Law, Law, Business & Economics Paper No. 20-11, Available at SSRN: https://ssrn.com/abstract=3549650

Jeffrey H. Kahn (Contact Author)

Harry M. Walborsky Professor, Florida State University College of Law; Associate Dean, Business Program ( email )

425 W. Jefferson Street
Tallahassee, FL 32306
United States
850.644.7474 (Phone)

HOME PAGE: http://www.law.fsu.edu/faculty/jkahn.html

John E. Lopatka

The Pennsylvania State University (University Park) – Penn State Law ( email )

Lewis Katz Building
University Park, PA 16802
United States

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