Expert Witness Testimony Landmark Cases in California

"California law permits a person with 'special knowledge, skill, experience, training, or education' in a particular field to qualify as an expert witness (Evid. Code, 720) and to give testimony in the form of an opinion (id., 801). Under Evidence Code section 801, expert opinion testimony is admissible only if the subject matter of the testimony is 'sufficiently beyond common experience that the opinion of an expert would assist the trier of fact.' (Id., subd. (a).) The subject matter of the culture and habits of criminal street gangs . . . meets this criterion." (People v. Gardeley (1996) 14 Cal.4th 605, 617; see also id. at p. 619 expert opinion that described attack would be "gang-related activity".) The prosecution may use hypothetical questions that track the evidence, even if only "thinly disguised," to establish that the crime was gang related. (People v. Vang (2011) 52 Cal.4th 1038, 1045.) "Although expert testimony is generally inadmissible on topics 'so common' that jurors of ordinary knowledge and education could reach a conclusion as intelligently as the expert, an expert may testify on a subject about which jurors are not completely ignorant. . In determining the admissibility of expert testimony, 'the pertinent question is whether, even if jurors have some knowledge of the subject matter, expert opinion testimony would assist the jury.' ." (People v. Lindberg (2008) 45 Cal.4th 1, 45.) "When expert opinion is offered, much must be left to the trial court's discretion." (People v. Carpenter (1997) 15 Cal.4th 312, 403.) "The trial court has broad discretion in deciding whether to admit or exclude expert testimony citation, and its decision as to whether expert testimony meets the standard for admissibility is subject to review for abuse of discretion. ." (People v. McDowell (2012) 54 Cal.4th 395, 426) "Expert testimony in the form of an opinion may be based on hearsay or facts outside the personal knowledge of the expert." (People v. Harris (2013) 57 Cal.4th 804, 847; Evid. Code, 801, subd. (b).) However, "an expert may not under the guise of stating reasons for an opinion bring before the jury incompetent hearsay evidence." (People v. Price (1991) 1 Cal.4th 324, 416.) "Because an expert's need to consider extrajudicial matters, and a jury's need for information sufficient to evaluate an expert opinion, may conflict with an accused's interest in avoiding substantive use of unreliable hearsay, disputes in this area must generally be left to the trial court's sound judgment." (People v. Montiel (1993) 5 Cal.4th 877, 919).) A trial court may cure a hearsay problem by a limiting instruction, or by excluding the evidence as irrelevant, unreliable, or potentially prejudicial under Evidence Code section 352. (Montiel, at p. 919.)