What is the impact of testimony by a domestic violence expert on a jury?

"When the trial testimony of an alleged victim of domestic violence is inconsistent with what the victim had earlier told the police, the jurors may well assume that the victim is an untruthful or unreliable witness. [Citations.] And when the victim's trial testimony supports the defendant or minimizes the violence of his actions, the jurors may assume that if there really had been abusive behavior, the victim would not be testifying in the defendant's favor. [Citations.] These are common notions about domestic violence victims . . . ." (People v. Brown, supra, 33 Cal.4th at p. 906.) Testimony by a domestic violence expert can help to overcome these common misperceptions. (Id. at p. 906-907.) Such expert opinion is not common knowledge.