Expert testimony is often critical to establish a claim or defense. Expert testimony is allowed where scientific, technical, or other specialized knowledge will assist the judge or jury to understand the evidence in a case or to determine a fact in issue involved. An expert witness must be qualified to render an opinion. In addition, an expert’s methodology and opinion must pass muster with the court–it must find them to be sufficiently valid and reliable.

Unlike an ordinary witness, an expert is given wide latitude to offer opinions, including opinions that are not based on firsthand knowledge or observation. This latitude is based on an assumption that the expert’s opinion will have a reliable basis in the knowledge and experience of his or her discipline.

In Daubert, the Supreme Court held that Federal Rule of Evidence 702 requires a trial judge to “ensure that any and all scientific testimony … is not only relevant, but reliable.” Thus, courts serve as a gatekeeper to ensure that an expert’s testimony rests “on a reliable foundation” and will be “relevant to the task at hand.”

In subsequent opinions, the court has made clear that the rule applies to all expert testimony.

Federal Rule of Evidence 702 provides:

If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise.

The Rule’s “reliability” standard applies to all “scientific,” “technical,” or “other specialized” matters within its scope. In the words of the Supreme Court, it “requires a valid … connection to the pertinent inquiry as a precondition to admissibility.” And where the testimony’s factual basis, data, principles, methods, or their application are called sufficiently into question, the trial judge must determine whether the testimony has “a reliable basis in the knowledge and experience of [the relevant] discipline.”

To qualify as an expert witness in a Texas court, a witness must: (1) be qualified and (2) their testimony must be relevant and based on a reliable foundation.

Qualification is evaluated by a review of the expert’s training and experience. The specialized knowledge that qualifies a witness to offer an expert opinion may be derived from specialized education, practical experience, a study of technical works, or a combination of these things. The expert’s background must be tailored to the specific area of expertise in which she desires to testify, and the proponent of the expert’s testimony has the burden to show that the witness is qualified on the matter in question. If a witness has a sufficient background in a particular field, then the trial court must then determine whether that background goes to the very matter on which the witness is to give an opinion.

Under Federal Rule of Evidence 702, a qualified witness may provide an opinion if the:

• Testimony is based on sufficient facts or data.
• Testimony is the product of reliable principles and methods.
• Expert reliably applied the principles and methods to the facts of the case.

An expert’s testimony must also satisfy certain criteria in order to be admissible. The Supreme Court’s opinion of Daubert v. Merrill Dow Pharmaceuticals is the seminal opinion governing the reliability analysis at the federal level. Under Daubert, the court identified the following non-exhaustive factors to evaluate whether the reasoning or methodology behind an expert’s opinion is sufficiently reliable:

1. Whether the theory or technique in question can be and has been tested;
2. Whether it has been subjected to peer review and publication;
3. Its known or potential error rate;
4. The existence and maintenance of standards controlling its operation;
5. Whether it has attracted widespread acceptance within a relevant scientific community.

Again, these standards also extend not only to experts who will testify on scientific issues, but also to testimony based on “technical” and “other specialized” knowledge. A trial judge has significant discretion in deciding in a particular case how to determine whether particular expert testimony is reliable. Courts consider the specific factors identified in Daubert where they are reasonable measures of the reliability of expert testimony.

Texas courts utilize a “modified Daubert” standard. The Texas Supreme Court has set forth the following non-exhaustive list of factors to determine whether an expert’s opinion is admissible in Texas courts:

1. the extent to which the theory has been or can be tested;
2. the extent to which the technique relies on the subjective interpretation of the expert;
3. whether the theory has been subjected to peer review and/or publication;
4. the technique’s potential rate of error;
5. whether the underlying theory or technique has been generally accepted as valid by the relevant scientific community; and
6. the non-judicial uses which may have been made of the theory or technique.

The Daubert standard is largely designed to keep “junk science” out of the courtroom and to help the trier of fact (the judge or jury) better understand aspects of the case. The more qualified the expert and the more reliable the method utilized to form the expert’s opinion, the more likely it is that the opinion or testimony will be admissible in court.

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