Excerpt from: The A-Z Guide to Expert Witnessing

An expert’s opinion may be challenged at a Daubert hearing. If the challenge is successful, the expert’s entire testimony could be excluded from evidence. This could result in the dismissal of the case and permanent damage to the reputation of the expert. What can an expert do to protect herself from a successful Daubert challenge?

General assessment

Prior to accepting the engagement, an expert should ask counsel if he anticipates a Daubert attack on the expert’s testimony. Next, the expert should evaluate for herself if a Daubert attack is likely. Is the case novel? Is it complex? Is a substantial amount in controversy? Was the case filed in federal court or in one of the majority of states that follow the Daubert Standard?

Specific criteria

The expert should take a long, hard look at her work and methodology results under the Daubert Standard. To avoid rejection of testimony, an expert should do the following.

–        Only use theories or techniques that have been tested and passed.

–        Use theories or techniques that are objective.

–        Specify the known error rate or potential error rate for the method.

–        Use methods with acceptable error rates.

–        Produce peer-reviewed literature (i.e., journal studies, reports, and treatises supporting the expert’s conclusions and opinions).

–        Produce reliable scientific data to prove that her methods and conclusions are generally accepted in the scientific community.

–        Demonstrate that her theories existed prior to the commencement of the litigation.

–        Not develop novel theories to support conclusions for specific litigation.

–        Demonstrate that she maintained standards and controls (for example, good laboratory practices and simultaneous blind controls).

–        Demonstrate that findings can and have been replicated by others.

–        Demonstrate that her methodology followed the scientific method as it is practiced by at least a recognized minority of scientists in her field.

–        Offer testimony that is sufficiently tied to the facts of the case to help the jury to resolve a factual dispute.

–        Avoid relying on the coincidence of temporality.

–        Avoid extrapolating unjustifiably from an accepted premise to an unfounded conclusion.

–        Adequately account for obvious alternative explanations.

–        Demonstrate the same care and accuracy as in regular professional work.

–        Use the real-world methodology of her field.

–        Use an appropriate methodology to ensure that her opinion derives from and constitutes a form of specialized knowledge.


Expert opinions must be supported by reliable methodology. “Junk science” may be excluded from evidence for being unreliable. Even if it is not excluded by the trial judge, the expert’s methodology may be subject to close questioning during cross-examination. Experts should base their opinions upon sound methodology. If an expert cannot base his opinion on a reliable methodology, he should decline to offer an opinion.