What is the test for allowing expert testimony in a medical malpractice case?

A trial court has broad discretion in allowing expert testimony and "[t]he trial court's decision on the admissibility of expert testimony [is] reviewed for an abuse of discretion or manifest error." United States v. Dorotich, 900 F.2d 192, 194 (9th Cir.1990). A conviction will not be reversed because of the erroneous exclusion of expert testimony unless the exclusion more likely than not materially affected the verdict. U.S. v. Binder, 769 F.2d 595, 601-602 (9th Cir.1985).