Legal Definitions - Daubert test

The Daubert test is a standard used by judges in federal courts (and most state courts) to determine whether expert testimony is reliable and relevant enough to be presented to a jury. Named after the landmark U.S. Supreme Court case Daubert v. Merrell Dow Pharmaceuticals, Inc., this test establishes the judge's role as a "gatekeeper" for expert evidence.

Before an expert witness can share their specialized knowledge with a jury, the judge must assess whether their testimony is based on sound scientific, technical, or other specialized principles and methods. The goal is to ensure that juries hear only expert opinions that are credible and well-founded, rather than speculative or unproven theories.

To make this determination, judges consider several flexible factors, including:

• Whether the expert's theory or technique can be (or has been) tested.
• Whether the theory or technique has been subjected to peer review and publication in scientific or professional journals.
• The known or potential rate of error of the technique, and the existence of standards controlling its operation.
• The degree to which the theory or technique has been generally accepted within the relevant scientific or professional community.

This scrutiny applies to all types of expert testimony, not just scientific evidence.

Here are some examples of how the Daubert test might be applied:

• Example 1: Product Liability Case

  Imagine a lawsuit where a plaintiff claims a new type of smart appliance malfunctioned and caused property damage. The plaintiff wants to introduce testimony from an engineer who developed a novel theory about a previously unknown type of electromagnetic interference causing the malfunction. This engineer's theory has not been published, peer-reviewed, or widely tested by others in the field.

  How the Daubert test applies: The judge would apply the Daubert test to determine if this engineer's testimony is admissible. The court would likely question whether the theory is testable, if it has undergone peer review, its known error rate, and its acceptance within the broader engineering community. If the judge finds the theory lacks sufficient scientific rigor and reliability based on these factors, the engineer's testimony would be excluded, preventing the jury from hearing an unproven and potentially misleading opinion.

• Example 2: Digital Forensics in a Cybercrime Trial

  In a complex cybercrime case, the prosecution seeks to introduce testimony from a digital forensics expert. This expert claims to have used a proprietary, newly developed software tool to recover encrypted data from a unique, custom-built server, and their analysis points to the defendant's involvement. The defense challenges the admissibility of this expert's findings.

  How the Daubert test applies: The judge would use the Daubert test to evaluate the reliability of the expert's methodology. The court would inquire about the new software tool's validation process, whether its underlying algorithms have been tested and peer-reviewed, its potential for error, and whether the techniques used are generally accepted within the digital forensics community for this type of server. If the expert cannot demonstrate the reliability and scientific validity of their novel tool and methods, their testimony might be deemed inadmissible.

• Example 3: Medical Causation in an Environmental Lawsuit

  A community sues a chemical plant, alleging that exposure to a specific, newly synthesized chemical released by the plant caused a rare cluster of health issues among residents. The plaintiffs present a medical expert who testifies that, based on their research, this chemical directly causes these specific health problems, even though there isn't extensive existing literature on this particular chemical's long-term human health effects.

  How the Daubert test applies: The judge would scrutinize the medical expert's methodology for establishing causation. The court would assess whether the expert's research linking the chemical to the health issues is testable, if it has been peer-reviewed, if there's a known error rate in their diagnostic or epidemiological methods, and the degree to which their conclusions are accepted by the broader medical and toxicology communities. If the expert's causal link is based on speculative or unvalidated scientific methods, their testimony could be excluded, as it wouldn't meet the reliability standards of the Daubert test.