What is the test for admitting expert testimony at trial?

would assist the trier of fact." (Evid. Code, 801, subd. (a).) An appellate court reviews the trial court's decision to admit expert testimony for abuse of discretion. (People v. Prince (2007) 40 Cal.4th 1179, 1223 (Prince).)

" '[T]he admissibility of expert opinion is a question of degree. The jury need not be wholly ignorant of the subject matter of the opinion in order to justify its admission; if that were the test, little expert opinion testimony would ever be heard. Instead, the statute declares that even if the jury has some knowledge of the matter, expert opinion may be admitted whenever it would "assist" the jury. It will be excluded only when it would add nothing at all to the jury's common fund of information, i.e., when "the subject of inquiry is one of such common knowledge that men of ordinary education could reach a conclusion as intelligently as the witness" ' [citation]." (People v. McAlpin (1991) 53 Cal.3d 1289, 1299-1300.)