California Supreme Court Rejects Exceptionally Poor Sampling Method, But Leaves Open Many Questions About Sampling And Class Certification

In Duran v. U.S. Bank N.A. (pdf), the California Supreme Court recently addressed an important question in the context of state-court class actions: Can plaintiffs invoke statistical sampling in an attempt to prove class-wide liability and overcome the presence of individual questions that ordinarily would defeat class certification?

The court's answer to that question is a mixed bag for business. The court firmly rejected the haphazard approach to sampling used by the trial court in the lawsuit against U.S. Bank. But the court left open the troubling possibility that sampling might be used in support of class certification in the future.

Why do plaintiffs try to use statistical sampling in the first place? To certify a class, plaintiffs must show that the elements of their claims can be proved for each class member by using common evidence. Common abstract questions are relatively easy to identify, but in many cases common answers are harder to come by. Even