Class Certification And Expert Witnesses

Christine Funk

Written by
— Updated on June 23, 2020

Class Certification And Expert Witnesses

Class Certification And Expert Witnesses

The Federal Rules of Civil Procedure dictate the prerequisites for class actions.  Class actions are limited to those cases wherein the following prerequisites have been met:

  1. The class is so numerous that joinder of all members is impracticable
  2. There are questions of law or fact common to the class
  3. The claims or defenses of the representative parties are typical of the claims or defenses of the class
  4. The representative parties will fairly and adequately protect the interests of the class.

Federal Rules of Civil Procedure 23 (a) 1-4.

Courts do not simply rubber stamp a plaintiff’s assertion that they meet the requirements for class certification.  Rather, the party seeking certification must prove the class has common questions of fact or law.  Wal-Mart Stores, Inc. v. Dukes, 131 S.Ct. 2541 (2011).  Expert witness testimony has become more and more important in determining whether class certification should be granted.

Relying on the Daubert Standard to Evaluate Expert Testimony

When seeking class certification, plaintiffs often offer expert testimony to support the requirements of Fed.R.Civ.Pro. 23 (a) (2), the issue of a common question of law or fact.  Courts are increasingly applying the Daubert factors in assessing whether the methodology relied upon by the expert is valid.  The Daubert factors include:

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

Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993).  While not specifically holding the Daubert analysis is necessary in evaluating whether an expert’s testimony is sufficient to establish the prerequisites for class actions, the Supreme Court has at least suggested this is, or should be, the case.  In Dukes, Justice Scalia, writing for the court, states, “The District Court concluded that Daubert did not apply to expert testimony at the certification stage of class action proceedings.  We doubt that is so. . . “  Dukes, at 2553 – 2554.

Approaches for Plaintiffs to Consider

When plaintiffs seek an expert to testify about class certification issues, there are several things to consider.

If you are able to do so, consider prior testimony of an expert before hiring one expert over another.  Viewing a recorded deposition will provide you with invaluable information about how an expert witness presents him or herself to the court.  Given the court will be making important credibility decisions about your expert and their opinions, selecting an expert who testifies with ease is an important first step.

Hiring a good testifier, however, is not a complete recipe for success.  You also need an expert with the credentials to back up their opinions.  Recall, one can testify as an expert if their “scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact at issue.”  Federal Rules of Evidence 702.  While an advanced education may be required for expert witness testimony in some instances, “other specialized knowledge” may be sufficient for other cases.

Evaluate your expert’s conclusions with a critical eye.  You should be your own gatekeeper, before giving the judge and the respondent the chance to criticize your expert’s opinion.  Read their report and make note of any questions you may have.  Ask your expert for clarification for any point you don’t understand or are confused about.  Make certain all underlying assumptions are first clearly delineated, and second, factually correct.  Mistakes such as failing to provide your expert key information or your expert misunderstanding a relevant fact can be fatal to your case.  By reviewing the expert’s opinion ahead of time, you give yourself the opportunity to remedy the situation by providing the additional information or correcting a factual misunderstanding.

Note: This is not to suggest you should dictate your expert’s opinion.  Quite the contrary.  This simply suggests that as the lawyer, you have a duty to make certain the expert is fully and correctly informed regarding the facts at issue.  Many a lawyer has falsely assumed an expert “didn’t need” certain information, only to discover – too late – that the information was in fact critical to an expert’s conclusions.  This approach seeks to avoid such a catastrophe.

Where the other side offers an expert opinion of their own, discuss this opinion with your expert.  If you do not feel your expert is best suited for the dual role of consulting expert and testifying expert, or if the opposing expert drifts into another field of expertise, consider hiring another expert to consult.  All expert opinions should be reviewed carefully. Missing, misunderstood, or misstated information are all areas of attack for discrediting the witness.

Approaches for Respondents to Consider

As defendants in a potential class action suit, an expert responding to the plaintiff’s expert on the issue of class certification is likely the only witness the respondent will call.  As such, hiring an expert with the right qualifications and the ability to withstand cross examination is critical.

Experts should be brought into the case as early as possible.  It is not uncommon for an attorney to misunderstand or underestimate the depth and breath of the expert issues.  By bringing in an expert early, the attorneys increase their chances of catching their errors or incorrect assumptions early enough to hire different or additional experts, once they fully understand the issues presented.  After all, for the purpose of Federal Rule 23 (a) (2), only a single common question is required to certify the class. Id.  If a plaintiff proceeds on multiple theories, or alternate theories, having more than one expert may be necessary to respond to each individual potential common question of fact or law.

An expert can assist in not only evaluating the conclusions of a plaintiff’s expert, but also in evaluating the soundness of their underlying assumptions about the case or facts.  Where the underlying assumptions are inaccurate or incomplete, the resulting data is necessarily questionable.  Thus, an expert in the field may provide another basis for denying class certification.

Experts can also help counsel prepare for cross examination of the opposing expert.  Experts are far more familiar with the most recent literature on the issue at hand (or lack thereof) than most attorneys.  They can assist in crafting questions in a logical and scientifically correct manner.  Additionally, having the expert in the courtroom during cross examination can lead to more forthcoming answers from the opposing witness, as well as the ability to instantly receive feedback during testimony.


In preparing for a class certification hearing, both sides would do well to retain and use experts to evaluate both their position and the position of the opposing party for the court.  Experts can offer their experience and knowledge to answer the critical question: whether there are common questions of law or fact.  Failure of plaintiffs to do so could result in the denial of class certification.  Failure of respondents to challenge a plaintiff’s expert could result in certification, even if later expert consultation reveals weaknesses or flaws in a plaintiff’s expert’s opinions.

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