Witnesses and Expert Testimony: Personal Knowledge, Rule 702 and Daubert

Competency and personal knowledge

Rule 601 begins: “Every person is competent to be a witness unless these rules provide otherwise.” Rule 602 then requires personal knowledge: “A witness may testify to a matter only if evidence is introduced sufficient to support a finding that the witness has personal knowledge of the matter.” Lay witnesses may give opinions only if they are rationally based on their own perception (Rule 701).

Expert testimony under Rule 702

A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if the proponent demonstrates to the court that it is more likely than not that: (a) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue; (b) the testimony is based on sufficient facts or data; (c) the testimony is the product of reliable principles and methods; and (d) the expert’s opinion reflects a reliable application of the principles and methods to the facts of the case.

Fed. R. Evid. 702 (as amended Dec. 1, 2023)

The 2023 amendment made clear that the party offering the expert must meet each requirement by a preponderance of the evidence.

The judge as gatekeeper

… under the Rules the trial judge must ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable.

Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 589 (1993)

Daubert replaced the older “general acceptance” test from Frye. Courts may consider factors such as testing, peer review, error rates and acceptance in the field.

Researching expert testimony in your state

To research expert testimony for a real matter, start with the primary sources. For example, read the statute, the rule and the documents in your own file. Then look for recent appellate decisions from your state, because they control how local courts read the law. After that, compare what you found with the federal rules that may also apply. Our state procedures guide and the Research Center can help you find and check each source.

Sources and further reading

Official sources used on this page:

• law.cornell.edu
• law.cornell.edu
• law.cornell.edu
• static.case.law

Related reading on Lawtopolis:

• The Hearsay Rule and Its Exceptions
• Relevance and the Federal Rules of Evidence: Rules 401, 402 and 403