As we touched on last summer,[1] whether a district court may certify a class action without resolving challenges to the admissibility of fact or expert evidence is still an unsettled question.  This question is particularly important with respect to expert evidence, given that class certification frequently hinges on competing experts’ opinions regarding the propriety of an aggregate action.  If an expert’s opinion is deemed inadmissible, the party proffering it is almost certain to be on the receiving end of an adverse certification ruling.