Chapter 2 - §11. Expert opinion

• Jurisdiction: United States

§11. Expert opinion

Expert testimony consists of a statement of opinion by a witness on a matter beyond the knowledge and experience of the ordinary layperson and for which the expert possesses special ability to provide such an opinion on the specific subject before the court. Evid. C. §801; see Evid. C. §720; People v. Killebrew (5th Dist.2002) 103 Cal.App.4th 644, 651, disapproved on other grounds, People v. Vang (2011) 52 Cal.4th 1038.

§11.1. Foundational requirements. For an expert's opinion to be admissible, the following foundation is required: (1) the subject matter must be sufficiently beyond common experience such that the opinion of an expert would assist the trier of fact, (2) the subject matter must have been perceived or personally known or made known to the witness at or before the hearing, (3) the opinion must be based on matter that is reasonably relied on by an expert in forming an opinion on the subject relating to her testimony, and (4) the witness must have special knowledge. See Evid. C. §801. The court has wide discretion on the subject of expert testimony, with any doubts going to the weight and not the admissibility of the testimony. See People v. Sanchez (2019) 7 Cal.5th 14, 46; see also People v. Krebs (2019) 8 Cal.5th 265, 323-24 (purported conflict between expert opinion and expert testimony given in other trials does not, as a matter of law, render that opinion false). Because they are allowed to give such opinions, experts are given greater latitude to testify about matters beyond their personal knowledge. People v. Valencia (2021) 11 Cal.5th 818, 836. Also, the court may limit the number of expert witnesses. Evid. C. §723; see Evid. C. §352.

Federal Comparison Under the FREs, a qualified expert witness can testify if "scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue." FRE 702. After an expert is duly qualified under the FREs through knowledge, skill, experience, training, or education, she can testify in the form of an opinion or otherwise. FRE 702. In this regard, FRE 702 is similar to Evid. C. §720(a), except that FRE 702 does not contain a parallel provision to Evid. C. §720(a) requiring that "[a]gainst the objection of a party, such special knowledge, skill, experience, training, or education must be shown before the witness may testify as an expert."

1. Subject matter beyond common experience. To be admissible, an expert's opinion must be related to a subject that is sufficiently beyond common experience such that it will assist the trier of fact. Evid. C. §801(a); People v. Tran (4th Dist.2020) 50 Cal.App.5th 171, 186. This does not require a finding that the jury be completely ignorant about the subject matter before the testimony can be admitted. People v. Fudge (1994) 7 Cal.4th 1075, 1121. Nor does it require that all parts of an expert's testimony be beyond the jury's common experience. E.g., People v. Rodriguez (2014) 58 Cal.4th 587, 639 (expert testimony about what causes rubber to fracture was sufficiently beyond common experience to be admissible even though parts of testimony referred to matters within common knowledge); see, e.g., People v. Dalton (2019) 7 Cal.5th 166, 236-37 (expert testimony that acid injected into vein would be more painful than acid injected into muscle was sufficiently beyond common experience to be admissible even though it is common knowledge that acid causes pain); People v. Sibrian (1st Dist.2016) 3 Cal.App.5th 127, 133-34 (expert testimony about police tactics and training as basis for evaluating officers' handling techniques and choice of assistive tools in resisting-officer case was sufficiently beyond common knowledge of bare-handed force). An expert's opinion testimony is improper only when it would add nothing at all to the jury's common source of information. Dalton, 7 Cal.5th at 237; People v. Lucas (2014) 60 Cal.4th 153, 230, disapproved on other grounds, People v. Romero (2015) 62 Cal.4th 1; People v. Jones (2012) 54 Cal.4th 1, 60; People v. Stoll (1989) 49 Cal.3d 1136, 1154. Thus, the expert's opinion need only be helpful, not necessary. See People v. Reardon (3d Dist.2018) 26 Cal.App.5th 727, 738-39; People v. Hopper (3d Dist.1956) 145 Cal. App.2d 180, 191-92. The critical determination is whether a person of ordinary education and knowledge could arrive at a conclusion as intelligently as the expert witness about the subject matter of the expert's opinion. People v. McAlpin (1991) 53 Cal.3d 1289, 1300. If such a conclusion can be drawn just as easily and intelligently by the trier of fact, the expert opinion is not admissible. People v. Valdez (6th Dist.1997) 58 Cal.App.4th 494, 506.

(1) Proper expert opinion. Proper areas of expert opinion in criminal cases include the following:

(a) Crime-scene reconstruction. People v. Farnam (2002) 28 Cal.4th 107, 162-63.

(b) The cause of a fire. See, e.g., Mason v. Superior Ct. (3d Dist.2015) 242 Cal.App.4th 773, 785-86 (arson expert permitted to give opinion as to cause of fire by relying on photographs, reports, and interviews without visiting scene of fire).

(c) The time and cause of death or injury as well as the circumstances surrounding it. People v. Mayfield (1997) 14 Cal.4th 668, 766, disapproved on other grounds, People v. Scott (2015) 61 Cal.4th 363; see People v. Bledsoe (1984) 36 Cal.3d 236, 249 (expert can give opinion that child's injuries were result of battered-child syndrome and not accidental); Bates v. Newman (2d Dist.1953) 121 Cal.App.2d 800, 803 (medical expert can give opinion about person's ability or inability to do certain acts); see, e.g., People v. Brown (2014) 59 Cal.4th 86, 100 (forensic pathologist gave opinion that sexual assault and drowning of victim occurred fairly concurrently); People v. Edwards (2013) 57 Cal.4th 658, 708-09 (pathologist who did not perform autopsy gave opinion that injuries occurred before death and were "highly painful"); People v. Taylor (2010) 48 Cal.4th 574, 588 (forensic pathologist gave opinion that injuries were consistent with forcible rape); People v. Robinson (2005) 37 Cal.4th 592, 631-32 (forensic pathologist gave opinion about where bodies were positioned during shooting). This includes opinion evidence on the nature of the wounds, including whether they were done defensively or deliberately. See, e.g., People v. Bemore (2000) 22 Cal.4th 809, 819 (opinion that wounds were defensive and indicated struggle); People v. Welch (1999) 20 Cal.4th 701, 750-51 (opinion that wounds indicated that killing was done deliberately), overruled on other grounds, People v. Blakeley (2000) 23 Cal.4th 82; People v. Cole (1956) 47 Cal.2d 99, 104-05 (opinion that fatal wound was not self-inflicted); People v. Jones (4th Dist.1993) 14 Cal.App.4th 1252, 1256 (opinion that wounds indicated that killing occurred during rage); People v. Bobo (3d Dist.1990) 229 Cal.App.3d 1417, 1426 (opinion that certain wounds were hesitation cuts).

(d) The character of a defendant, victim, or witness. See "Character & Related Evidence," ch. 4-A, §1 et seq.

(e) The sanity of the defendant. See People v. Williams (1988) 44 Cal.3d 883, 902-03; see also People v. Jantz (2d Dist.2006) 137 Cal.App.4th 1283, 1295 (D waives privilege against self-incrimination and right to counsel regarding expert testimony in sanity trial when D voluntarily places his mental condition in issue).

(f) The existence of a mental illness, disorder, or defect as long as the testimony tends to show that the defendant did or did not actually have the required mental state, and as long as the expert does not offer the opinion that the defendant actually did or did not harbor the required mental state. People v. Herrera (2d Dist.2016) 247 Cal. App.4th 467, 475-76; People v. Cortes (6th Dist.2011) 192 Cal.App.4th 873, 908; see, e.g., People v. DeHoyos (2013) 57 Cal.4th 79, 121 (asking expert whether he believed D understood difference between right and wrong when D killed victim did not seek evidence of D's capacity).

(g) The general psychological factors that could lead a person to make a false confession to law enforcement. See People v. Page (1st Dist.1991) 2 Cal.App.4th 161, 187-88 (expert can testify to factors that may affect reliability of confession, but expert cannot give opinion on whether confession in case was in fact involuntary).

(h) The general psychological factors that could affect the accuracy of eyewitness identification. E.g., People v. McDonald (1984) 37 Cal.3d 351, 368-69 (although jurors may not be totally unaware of psychological factors that bear on eyewitness identification, body of information now available is sufficiently beyond common experience), overruled on other grounds, People v. Mendoza (2000) 23 Cal.4th 896. But see People v. Wright (1988) 45 Cal.3d 1126, 1142 n.13 (psychological factors affecting eyewitness identifications are sufficiently experimental and open to debate that most courts are reluctant to admit expert testimony on the subject); People v. Johnson (1st Dist.1993) 19 Cal. App.4th 778, 786-87 (questioning whether permitting expert psychologist's testimony about another witness's credibility is desirable as practical matter). The decision to admit or exclude expert testimony on eyewitness identification is a matter that is primarily within the court's discretion. Lucas, 60 Cal.4th at 276-77; McDonald, 37 Cal.3d at 377. But when eyewitness identification of the defendant is a key element of the prosecution's case, the identification is not substantially corroborated by evidence giving it independent reliability, and the defendant offers expert testimony on specific psychological factors beyond the jury's common experience that bear on the accuracy of the identification, it will ordinarily be error if the court excludes that testimony. McDonald, 37 Cal.3d at 377; see Lucas, 60 Cal.4th at 277; People v. Chavez (4th Dist.2018) 22 Cal.App.5th 663, 680; see, e.g.,...