What is the test for the admissibility of expert opinions in medical malpractice cases?

⁶ People v. Dejourney(2011) 192 Cal.App.4th 1091, 1110, 121 Cal.Rptr.3d 787 ("Because admissibility of expert opinion is a question of degree, and a jury need not be wholly ignorant of the subject matter under the statutory rule, exclusion is only necessary where the opinion would add nothing at all to the jury's common fund of information.").