The tactic is more common that one might imagine: when plaintiffs file their motion for certification, they may include an expert report from a noted law professor, testifying that their case is ideally suited for certification under Rule 23. Now, on one side of the certification debate, you have practicing lawyers zealously representing their client, and on the other, a ostensibly neutral expert in civil procedure. How can a defendant effectively oppose a motion like this?

By excluding the expert, which is easier than it first appears. Take the case of Walsh v. Principal Life Insurance Co., 266 F.R.D. 232 (S.D. Iowa 2010). In this ERISA class action, the plaintiff alleged that the the defendants had violated the statute by persuading her (after letting her go from her job) to roll over her 401(k) [] contributions in order to buy their "proprietary" investment products.

To support her motion for class certification, the plaintiff offered two experts: Robert Klonoff, Dean of Lewis & Clark Law School in Oregon, and Mark Johnson, a "sought-after speaker on the topic of ERISA and benefits plans." She offered each expert to testify about how the case had met the standards of Rule 23. The defendants challenged the admissibility of both experts’ testimony. They did not question their expertise on ERISA or Rule 23. (Nor could they credibly. Dean Klonoff, for example, is the author of Class Actions and Other Multi-Party Litigation in a Nutshell, and co-author of the casebook Class Actions and Other Multi-party Litigation: Cases And Materials.). But they did point out that both experts had been offered to testify about a legal conclusion: whether certification was appropriate in this case. And that is the one area for which expert testimony is not admissible because it cannot help the court. The court largely agreed:

"[E]xpert testimony on legal matters is not admissible. Matters of law are for the trial judge, and it is the judge’s job to instruct the jury on them." S. Pine Helicopters, Inc. v. Phoenix Aviation Managers, Inc., 320 F.3d 838, 841 (8th Cir. 2003) (citing United States v. Klaphake, 64 F.3d 435, 438-39 (8th Cir. 1995)); see also Burkhart v. Washington Metro. Area Transit Auth., 112 F.3d 1207, 1213, 324 U.S. App. D.C. 241 (D.C. Cir. 1997) ("Each courtroom comes equipped with a ‘legal expert’ called a judge."). In distinguishing admissible testimony from inadmissible testimony, the task for the Court is to ask whether the expert’s opinions bear on some factual inquiry or whether they bear solely on the legal conclusions that are urged. In other words, "an expert may offer his opinion as to facts that, if found, would support a conclusion that the legal standard at issue was satisfied, but he may not testify as to whether the legal standard has been satisfied." 

(Internal quotations left in to preserve the Burkhart parenthetical.) The court did find that Johnson had made some factual observations about ERISA plans, so it allowed his testimony for that limited purpose.  Then it denied plaintiff’s motion for certification, because the question of how the defendants persuaded each class member was necessarily individualized.

So what’s the takeaway in this case? When faced with an "expert" on Rule 23, remember: "Each courtroom comes equipped with a ‘legal expert’ called a judge." And his is the only opinion that matters.

[Full disclosure: Dean Klonoff very generously provided a blurb for The Class Action Playbook (first under Editorial Reviews).]