elaxing the traditional barriers to `opinion' testimony." Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 5 EFTA00088807 579, 588 (1993) (quoting Beech Aircraft Cap. v. Rainey, 488 U.S. 153, 169 (1988)). Under Daubert, a district court must first determine whether an expert is qualified. See Fed. R. Evid. 702 (