Evidence Code Section 721: The Sword and Shield (Mostly Sword) for Expert Witness Cross-Examination

Apr 08, 2020

"I know lots of people who say you're wrong!" 

"Really? Like who?" 

"Well, you know ... like ... lots of people."

The proverbial "they" as in, "You know what they say ..." Is among the laziest rejoinders in an argument. Instead of identifying problems of fact or logic, the person invents an imaginary consensus to suggest his or her opponent's position is nothing but a fringe outlier.

Certainly such a tactic has no place in the courtroom, right? After all, one of the main reasons to exclude hearsay is to preclude the admission of factual assertions without the safeguard of cross-examination. 

Evidence Code section 721 provides the parameters of allowable cross-examination for expert witnesses. Its provisions leave enough wiggle room that unwary litigators can leave their expert vulnerable to cross-examination with untested hearsay. Understanding Section 721 and its scope is imperative for proper expert witness discovery and trial examinations.   


Breadth of Cross-Examination of Expert Witnesses 

When it comes to cross-examining expert witnesses, the permitted scope is much broader than percipient witnesses. "Once an expert offers his opinion ... he exposes himself to the kind of inquiry which ordinarily would have no place in the cross-examination of a factual witness." Hope v. Arrowhead & Puritas Waters, Inc., 174 Cal. App. 2d 222, 230 (1959). As explained in Monroy v. City of Los Angeles, 164 Cal. App. 4th 248, 267 (2008), "[w]hile there can be no hard and fast rule regarding the limits of cross-examination, a trial court's rulings should not be so overly restrictive as to deprive trial counsel of the tools necessary to probe, test, and even discredit the adverse expert witness." (Emphasis added). 

But what are the "tools necessary" to cross-examine an expert witness? In California, Evidence Code section 721 is the Leatherman of the cross-examiner's various tools.  

Monroy explained that "[t]he successful cross-examiner will attack not only the opinions and conclusions of the expert but also the factual underpinnings and rationale used by the expert in forming them." Id. This requires "repetitive questions" and sometimes "asking the same question in different styles and ways." Id. Likewise, testing the "foundational facts and the use of hypothetical questions" may be necessary to show that "the expert's opinion is untenable, illogical, or inapt under the facts of the particular case being litigated." Id. The statutory authority for this expanded scope of cross-examination is found in Section 721. Section 721(a) expressly identifies the additional grounds upon which an expert may be cross-examined: 

Of course, like any Evidence Code section, Section 721 must be read in the context of other, potentially competing sections. Take hearsay, for example. The general rule of inadmissibility when it comes to hearsay is the desire to exclude testimony that cannot be tested through cross-examination. See e.g., Target Natl. Bank v. Rocha, 216 Cal. App. 4th Supp. 1, 7 (2013) ("The basic theory is that the many possible deficiencies, suppressions, sources of error and untrustworthiness, which lie underneath the bare untested assertion of a witness, may be best brought to light and exposed by the test of cross-examination."). 

Section 721(b) is intended to provide a Goldilocks-type framework where (1) the cross-examination of an expert can remain robust, but (2) experts are not unfairly blindsided by the introduction of untested hearsay evidence that might challenge their opinions. Section 721(b) provides that "[i]f a witness testifying as an expert testifies in the form of an opinion, he or she may not be cross-examined in regard to the content or tenor of any scientific, technical, or professional text, treatise, journal, or similar publication unless[:]"

(1) The witness referred to, considered, or relied upon such publication in arriving at or forming his or opinion. 

(2) The publication has been admitted in evidence.

(3) The publication has been established as a reliable authority by the testimony or admission of the witness or by other expert testimony or by judicial notice. 

If admitted, relevant portions of the publication may be read into evidence but may not be received as exhibits. 

 Cal. Evid. Code § 721(b). 
The Comment to Section 721 explains that the desired purpose behind subdivision (b) is to hit the sweet spot between, on the one hand, adequately testing an expert witness and, on the other, introducing a competing opinion that cannot be safeguarded through cross-examination: 

If an expert witness has relied on a particular publication in forming his opinion, it is necessary to permit cross-examination in regard to that publication in order to show whether the expert correctly read, interpreted, and applied the portions he relied on. Similarly, it is important to permit an expert witness to be cross-examined concerning those publications referred to or considered by him even though not specifically relied on by him in forming his opinion. An expert's reasons for not relying on particular publications that were referred to or considered by him while forming his opinion may reveal important information bearing upon the credibility of his testimony. However, a rule permitting cross-examination on technical treatises not considered by the expert witness would permit the cross-examiner to utilize this opportunity not for its ostensible purpose--to test the expert's opinion--but to bring before the trier of fact the opinions of absentee authors without the safeguard of cross-examination.

Cal. Evid. Code § 721, Comment. 

But as explained below, Section 721(b) provides the potential to permit exactly what the Comment cautions against. Especially when it comes to subdivision (b)(3), an expert witness can be cross-examined with a third-party publication so long as some other expert testifies that the source is reliable. 

Section 721(b)(1): Cross-Examining the Expert on Materials "Considered"

California's Supreme Court has explained that "[t]he scope of cross-examination permitted under section 721 is broad, and [it] includes examination aimed at determining whether the expert sufficiently took into account matters arguably inconsistent with the expert's conclusion." People v. Ledesma, 39 Cal. 4th 641, 699 (2006). An easy application of Section 721(b)(1) occurs when an expert takes the stand and testifies "My opinion is that the rocket at issue was travelling 500 miles per hour at lift-off. My opinion is based on the treatise, Rocket Science." The more difficult questions occur when the expert more vaguely acknowledges what was "referred to, considered, or relied upon" in forming his or her opinions. 

Ledesma explained that the cross-examination is not limited to only those portions the expert "referred to, considered, or relied upon." Id. at 696, citing People v. Combs, 34 Cal. 4th 821, 893 - 894 ("We rejected the defendant's argument that the defense experts could be cross-examined only as to those portions of [the expert's] report that they had adopted and relied upon.").    

In People v. Clark, 5 Cal. 4th 950 (1993), California's Supreme Court explained that an expert who generalizes the bases for his or her opinion opens the door to a broad cross-examination. In Clark, the defendant was sentenced to death following a jury trial for rape and first-degree murder. In Clark's defense, Dr. Stephen Raffle, a psychiatrist and professor of medicine at the University of California, San Francisco, opined that Clark suffered various psychiatric disorders at the time of the murder. Dr. Raffle testified that Clark suffered a "rage reaction and disassociative state (i.e., a short break from reality) at the time of the crimes." Id. at 1115.  

On cross-examination, Dr. Raffle testified that he (1) "considered or relied upon all of his training in arriving at his conclusions[,]." and (2) was familiar with the writings of another psychiatrist, Dr. Bernard Diamond. Id. at 1139. The prosecutor then used an article by Dr. Diamond, entitled "With Malice Afterthought" and a portion of the article was read to the jury during the cross-examination. Id.

The Court held that cross-examination using Dr. Diamond's article was proper and consistent with Section 721(b) because Dr. Raffle acknowledged that he "considered or relied upon all of his training at arriving at his conclusions." Included in his training was familiarity with Dr. Diamond's article. It was thus fair game for cross-examination.   

The "Old" Section 721(b): McGarity v. Department of Transportation 

Section 721(b)(3) was added by amendment in 1997. Subdivision (b)(3) provides that cross-examination is permissible if "[t]he publication has been established as a reliable authority by the testimony or admission of the witness or by other expert testimony or by judicial notice." This allows an expert to be cross-examined with any text, even if the expert on the stand does not recognize the publication as authoritative, so long as some expert testifies that it is. To understand the breadth of this amendment, it is worth looking at an opinion that pre-dated it.

McGarity v. Department of Transportation, 8 Cal. App. 4th 677 (1992) was a personal injury and wrongful death lawsuit arising from a car accident allegedly caused by a dangerous condition on a public road. The plaintiff Michael McGarity was driving a 1973 Chevrolet pickup along a winding road with Myles Park as his passenger. Id. at 680. At one point, the road curved to the left at a ninety-degree angle and the curve warning sign that was supposed to be posted was not present. Id. Also missing from the road were reflective curve delineators; there were four on the road whereas the relevant traffic manual called for twelve. Id. 

Just before Mr. McGarity approached the curve, "the truck hit a bump in the road, momentarily distracting McGarity's attention." Id. Mr. McGarity drove off the road and the truck traveled 185 feet before hitting a concrete irrigation watergate. The watergate scraped the underside of the truck, "squashing the fuel tank 'like a milk carton.'" Id. The fuel tank ignited and engulfed the truck in flames. Mr. McGarity and Myles Park both suffered severe burns and Mr. Park later died from his injuries. Id. Mr. McGarity and representatives of Mr. Park's estate sued the State of California, Department of Transportation ("the State").   

Among the issues in dispute was the speed of the truck when it approached the curve. An eyewitness testified that he had been driving 80 miles per hour behind Mr. McGarity for about fifteen miles before the accident but had not closed the gap between their two vehicles. Id. The defendant's expert opined at trial that Mr. McGarity was driving 80 miles per hour at the time the truck left the road. Id. at 681. 

The plaintiffs' lawyer wished to cross-examine the State's expert witness using a crash test report "prepared by General Motors in a test crash at 30 miles per hour with a test truck of the same year and design but heavier than the accident vehicle." Id. The State objected, citing California Evidence Code section 721(b) (which at the time, did not include subdivision (b)(3)). 

The trial court sustained the State's objection and the plaintiffs appealed. For purposes of appeal, the Court explained that it is undisputed that the witness had not referred to, considered, or relied on the General Motors report in forming his opinion, nor had the report been admitted into evidence. Nevertheless, the plaintiffs argued that Section 721(b) did not apply because the General Motors crash test report was not a "text, treatise, journal, or similar publication." While the parties agreed that the report was indeed not a text, treatise or journal, the issue was whether it was a "similar publication." The plaintiffs argued that because the report was not published for "mass consumption ... section 721(b) [was] inapplicable." Id. at 682. The Court disagreed. The court explained that "the purpose of section 721(b) supports a broad construction of the term." Id.

The broad construction notwithstanding, the court explained that "to counterbalance the broad scope of cross-examination, the purpose of section 721(b) is 'to prevent an adverse party from getting before the trier of fact the inadmissible hearsay views of an absent expert, which may be contrary to the expert witness' opinion, through the device of cross-examining the expert witness regarding the absent expert's publication or report even though the testifying expert had not used or considered that publication or report in any way in arriving at or forming his opinion testimony.'" Id. at 683, citing 2 Jefferson, Evidence Benchbook (2d. ed. 1982) § 29.8, p. 1036, original emphasis.

The Court went on to explain the danger of allowing contrary opinions to make their way into evidence without the ability to test them through cross-examination: 

[A] rule permitting cross-examination on technical treatises not considered by the expert witness would permit the cross-examiner to utilize this opportunity not for its ostensible purpose—to test the expert's opinion—but to bring before the trier of fact the opinions of absentee authors without the safeguard of cross-examination. Although the court would be required upon request to caution the jury that the statements read are not to be considered evidence of the truth of the propositions stated, there is a danger that at least some jurors might rely on the author's statements for this purpose. Yet, the statements in the text might be based on inadequate background research, might be subject to unexpressed qualifications that would be applicable to the case before the court, or might be unreliable for some other reason that could be revealed if the author were subject to cross-examination.

Id. at 683 - 684, citing Cal. Law Revision Com. com., 29B West's Ann. Evid. Code (1966 ed.) § 721. 

Section 721(b)(3): Allowing an Even Broader Scope of Cross-Examination 

As explained in Establishing Reliability Under California Evidence Code Section 721(b)(3): Why California's Evidentiary Law Could Use More Consistency, 45 Cal. W. L. Rev. 475, 483 (Spring 2009), the legislative intent behind section 721 “indicates that the purpose of California Evidence Code section 721 is no longer simply to impeach expert testimony but also to counter opposing expert opinions." The article further states that “the purpose of the amendment is to allow learned treatises to substitute for live expert testimony, thus changing the original purpose of the rule, as well as the safeguards imposed by the hearsay rule.” Id. (Emphasis added). 

To illustrate, if another expert in McGarity testified that the crash test report prepared by General Motors was reliable authority, subdivision (b)(3) suggests a different outcome would have resulted. The Court already held that the report was a "similar publication." Accordingly, so long as another expert testified that the report was "established as a reliable authority" it would have been fair game for cross-examination (whether or not the State's expert witness had considered or relied on the report).  


The expert who boldly asserts that his or her opinion is based on all prior training and experience can open a wide door of cross-examination. The moment a witness acknowledges that a third-party publication (within the scope of Section 721(b)(1)) is among that prior training, it is fair game for cross-examination. In addition, having the opposing expert identify the reliable authorities at his or her deposition can help prevent a blindsiding cross-examination of your own expert. Section 721 is an important statute and its potency should not be overlooked.

David Sugden is a shareholder at Call & Jensen in Newport Beach, California.

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