Holding that, under the abuse-of-discretion standard, "we must affirm unless . . . the district court has made a clear error of judgment, or has applied the wrong legal standard"
Holding that "[t]he failure of [plaintiff's] experts to test their hypotheses in a timely and reliable manner or to validate their hypotheses by reference to generally accepted scientific principles as applied to the facts of this case renders their testimony on [causation] unreliable and therefore inadmissible under Daubert and Federal Rules of Evidence 702 and 104"