How does expert opinion work in a medical malpractice trial?

To be admissible, expert opinion testimony must be related to a subject sufficiently beyond common experience so that the opinion would assist the trier of fact. (Evid. Code, 801, subd. (a).) Expert opinion is not admissible if it consists of inferences and conclusions which can be drawn as easily by the trier of fact as by the expert. (People v. Torres (1995) 33 Cal.App.4th 37, 45.) The trial court should admit expert testimony that aids the jury because it references matters requiring some expertise, but should exclude testimony if it addresses matters the jury can understand and judge for itself. (People v. Smith (2003) 30 Cal.4th 581, 628.)