Does the jury have any authority to determine the credibility of an expert?

But jurors are called upon to judge the credibility of witnesses, including experts, based on such factors as the witness' demeanor. That the factors used by jurors are not easily articulated or do not appear on the record does not mean the determination is arbitrary or the result of personal biases. Our system of justice is based on trust in the ability of the finder of fact, whether judge or jury, to properly assess the credibility of experts. (See People v. Mayes (1988) 202 Cal.App.3d 908, 918-919, 248 Cal.Rptr. 899.) There is simply no reason to believe that the jurors were any less qualified to judge the credibility of expert witnesses in this case than in any other.