CACI No. 219. Expert Witness Testimony
Judicial Council of California Civil Jury Instructions (2024 edition)
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219.Expert Witness Testimony
During the trial you heard testimony from expert witnesses. The law
allows an expert to state opinions about matters in the expert’s field of
expertise even if the expert has not witnessed any of the events involved
in the trial.
You do not have to accept an expert’s opinion. As with any other
witness, it is up to you to decide whether you believe the expert’s
testimony and choose to use it as a basis for your decision. You may
believe all, part, or none of an expert’s testimony. In deciding whether to
believe an expert’s testimony, you should consider:
a. The expert’s training and experience;
b. The facts the expert relied on; and
c. The reasons for the expert’s opinion.
New September 2003; Revised May 2020
Directions for Use
This instruction should not be given for expert witness testimony on the standard of
care in professional malpractice cases if the testimony is uncontradicted.
Uncontradicted testimony of an expert witness on the standard of care in a
professional malpractice case is conclusive. (Howard v. Owens Corning (1999) 72
Cal.App.4th 621, 632-633 [85 Cal.Rptr.2d 386]; Conservatorship of McKeown
(1994) 25 Cal.App.4th 502, 509 [30 Cal.Rptr.2d 542]; Lysick v. Walcom (1968) 258
Cal.App.2d 136, 156 [65 Cal.Rptr. 406].) In all other cases, the jury may reject
expert testimony, provided that the jury does not act arbitrarily. (McKeown, supra,
25 Cal.App.4th at p. 509.)
Do not use this instruction in eminent domain and inverse condemnation cases. (See
Aetna Life and Casualty Co. v. City of Los Angeles (1985) 170 Cal.App.3d 865, 877
[216 Cal.Rptr. 831]; CACI No. 3515, Valuation Testimony.)
For an instruction on hypothetical questions, see CACI No. 220, Experts - Questions
Containing Assumed Facts. For an instruction on conflicting expert testimony, see
CACI No. 221, Conflicting Expert Testimony.
Sources and Authority
• Qualification as Expert. Evidence Code section 720(a).
• “ ‘A properly qualified expert may offer an opinion relating to a subject that is
beyond common experience, if that expert’s opinion will assist the trier of fact.’
‘However, even when the witness qualifies as an expert, he or she does not
possess a carte blanche to express any opinion within the area of expertise.
[Citation.] For example, an expert’s opinion based on assumptions of fact
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without evidentiary support [citation], or on speculative or conjectural factors
[citation], has no evidentiary value [citation] and may be excluded from
evidence. [Citations.] Similarly, when an expert’s opinion is purely conclusory
because unaccompanied by a reasoned explanation connecting the factual
predicates to the ultimate conclusion, that opinion has no evidentiary value
because an “expert opinion is worth no more than the reasons upon which it
rests.” ’ ‘An expert who gives only a conclusory opinion does not assist the jury
to determine what occurred, but instead supplants the jury by declaring what
occurred.’ ” (Property California SCJLW One Corp. v. Leamy (2018) 25
Cal.App.5th 1155, 1163 [236 Cal.Rptr.3d 500], internal citation omitted.)
• “Under Evidence Code section 720, subdivision (a), a person is qualified to
testify as an expert if he or she ‘has special knowledge, skill, experience,
training, or education sufficient to qualify him as an expert on the subject to
which his testimony relates.’ ‘[T]he determinative issue in each case must be
whether the witness has sufficient skill or experience in the field so that his
testimony would be likely to assist the jury in the search for the truth . . . .
[Citation.] Where a witness has disclosed sufficient knowledge, the question of
the degree of knowledge goes more to the weight of the evidence than its
admissibility. [Citation.]’ ” (Lattimore v. Dickey (2015) 239 Cal.App.4th 959, 969
[191 Cal.Rptr.3d 766].)
• The “credibility of expert witnesses is a matter for the jury after proper
instructions from the court.” (Williams v. Volkswagenwerk Aktiengesellschaft
(1986) 180 Cal.App.3d 1244, 1265 [226 Cal.Rptr. 306].)
• “[U]nder Evidence Code sections 801, subdivision (b), and 802, the trial court
acts as a gatekeeper to exclude expert opinion testimony that is (1) based on
matter of a type on which an expert may not reasonably rely, (2) based on
reasons unsupported by the material on which the expert relies, or (3)
speculative. Other provisions of law, including decisional law, may also provide
reasons for excluding expert opinion testimony. [¶] But courts must also be
cautious in excluding expert testimony. The trial court’s gatekeeping role does
not involve choosing between competing expert opinions.” (Sargon Enterprises,
Inc. v. University of Southern California (2012) 55 Cal.4th 747, 771−772 [149
Cal.Rptr.3d 614, 288 P.3d 1237], footnote omitted.)
• “ ‘Generally, the opinion of an expert is admissible when it is “[r]elated to a
subject that is sufficiently beyond common experience that the opinion of an
expert would assist the trier of fact . . . .” [Citations.] Also, “[t]estimony in the
form of an opinion that is otherwise admissible is not objectionable because it
embraces the ultimate issue to be decided by the trier of fact.” [Citation.]
However, “ ‘Where the jury is just as competent as the expert to consider and
weigh the evidence and draw the necessary conclusions, then the need for expert
testimony evaporates.’ ” ’ Expert testimony will be excluded ‘ “ ‘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.” ’ ” ’ ” (Burton
EVIDENCE CACI No. 219
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v. Sanner (2012) 207 Cal.App.4th 12, 19 [142 Cal.Rptr.3d 782], internal citations
omitted.)
• Under Evidence Code section 801(a), expert witness testimony “must relate to a
subject that is sufficiently beyond common experience that the opinion of an
expert would assist the trier of fact.” (New v. Consolidated Rock Products Co.
(1985) 171 Cal.App.3d 681, 692 [217 Cal.Rptr. 522].)
• Expert witnesses are qualified by special knowledge to form opinions on facts
that they have not personally witnessed. (Manney v. Housing Authority of The
City of Richmond (1947) 79 Cal.App.2d 453, 460 [180 P.2d 69].)
• “Although a jury may not arbitrarily or unreasonably disregard the testimony of
an expert, it is not bound by the expert’s opinion. Instead, it must give to each
opinion the weight which it finds the opinion deserves. So long as it does not do
so arbitrarily, a jury may entirely reject the testimony of a plaintiff’s expert, even
where the defendant does not call any opposing expert and the expert testimony
is not contradicted.” (Howard, supra, 72 Cal.App.4th at p. 633, citations
omitted.)
• “When any expert relates to the jury case-specific out-of-court statements, and
treats the content of those statements as true and accurate to support the expert’s
opinion, the statements are hearsay. It cannot logically be maintained that the
statements are not being admitted for their truth.” (People v. Sanchez (2016) 63
Cal.4th 665, 686 [204 Cal.Rptr.3d 102, 374 P.3d 320].)
• “Any expert may still rely on hearsay in forming an opinion, and may tell the
jury in general terms that he did so. Because the jury must independently
evaluate the probative value of an expert’s testimony, Evidence Code section 802
properly allows an expert to relate generally the kind and source of the ‘matter’
upon which his opinion rests. A jury may repose greater confidence in an expert
who relies upon well-established scientific principles. It may accord less weight
to the views of an expert who relies on a single article from an obscure journal
or on a lone experiment whose results cannot be replicated. There is a distinction
to be made between allowing an expert to describe the type or source of the
matter relied upon as opposed to presenting, as fact, case-specific hearsay that
does not otherwise fall under a statutory exception.” (People v. Sanchez,supra,
63 Cal.4th at pp. 685-686, original italics.)
Secondary Sources
1 Witkin, California Evidence (5th ed. 2012) Opinion Evidence, §§ 26-44
Jefferson, California Evidence Benchbook (3d ed. 1997) §§ 29.18-29.55
1 Levy et al., California Torts, Ch. 3, Proof of Negligence, § 3.04 (Matthew Bender)
3A California Trial Guide, Unit 60, Opinion Testimony, § 60.05 (Matthew Bender)
California Products Liability Actions, Ch. 4, The Role of the Expert, § 4.03
(Matthew Bender)
48 California Forms of Pleading and Practice, Ch. 551, Trial, §§ 551.70, 551.113
(Matthew Bender)
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© Judicial Council of California.
