Examining Expert Witnesses in the Post-Sanchez Era

In People v. Sanchez, 63 Cal. 4th 665 (2016), the California Supreme Court decided that an expert witness cannot relay hearsay that communicates case-specific facts to the jury. This post examines how trial lawyers can and should examine expert witnesses in the post-Sanchez era. 

As a starting point, practitioners should master familiarity with Evidence Code section 801. Section 801 sets forth the allowable limits on which expert witnesses may offer opinions as well as the allowable bases for opinions. The section begins by stating that, "[i]f a witness is testifying as an expert, his testimony in the form of an opinion is limited to such an opinion as is...." Subdivision (b) then identifies the allowable bases, and this is where Sanchez issues arise. 

The language of subdivision (b) is set forth below. The key terms are separated by parentheses for purposes of this post's discussion:  

801. If a witness is testifying as an expert, his testimony in the form of an opinion is limited to such an opinion as is:

(b) [1] Based on matter (including his special knowledge, skill, experience, training, and education);

[2] [a] [P]erceived by [the expert witness] or personally known to the [expert] witness or

[2] [b] [i] [M]ade known to him at or before the hearing,

[ii] [W]hether or not admissible; 

[iii] [T]hat is of a type that reasonably may be relied upon by an expert in forming an opinion upon the subject to which his testimony relates; 

[3] [U]nless an expert is precluded by law from using such matter as a basis for his opinion.

Distinguish Between Facts "Personally Known" Versus "Made Known" to the Expert Witness 

Section 801(b) provides that an expert witness may offer opinions based on "matter" that is either (1) "perceived by or personally known to the witness," or (2) "made known to him at or before the hearing." Understanding this distinction is important for both the preparation of your own expert witness and the opposition of your adversary's. 

Let us first look at strategies when opposing your adversary's expert witness. In the vast majority of trials, a retained expert basis his opinion on matter "made known to him at or before the hearing[,]" and not on matter "perceived by or personally known to [him]." See Cal. Evid. § 801(b). To be certain, an expert witness basing his opinions on the review of deposition transcripts, key documents, and interviews is not opining on matters "perceived by or personally known" to him. A matter "perceived by or personally known" is where, for example, an expert personally witnessed an accident and offered an opinion about the speed of the car.  

Because most experts base their opinions on their review of documents and interviews, their opinions are based on "matter made known to him ... before the hearing." And once an adversary's expert witness starts identifying these types of "matter[s]," practitioners need to be sharply on the lookout for Sanchez violations. It is not uncommon for seasoned expert witnesses to use the most benign questions as opportunities to weave case-specific hearsay into their answers.

A 2017 trial where I defended an employer in a wrongful termination action provides a couple examples. The plaintiff retained an expert to opine on her emotional damages. The expert was asked about his review of the plaintiff's deposition transcript. While this was an example of the witness being asked about hearsay, I did not object because so much of the plaintiff's deposition was going to be used during her cross-examination (as well as the cross-examination of the expert), that I was content to have the expert admit his reliance on it.

However, one of the issues in the case was whether the plaintiff put her employer on notice of her daughter's alleged health issues during her employment (we contended she had not). And while plaintiff had sent a series of self-serving emails after her employment ended, the court had properly ruled that these emails were inadmissible hearsay. But watch how the expert tries to introduce the contents of these hearsay emails and relay case-specific facts to the jury, and see how the trial judge deals with the objection:

Q  What did you learn from [the plaintiff's] deposition?

A Well, these are depositions. So she did in her deposition -- this is just consistent with what she told me. She was asking about this part-time thing. She was worried about her milk, according to her. There's records of at that time she was writing about this. The HR person ... was informed of these health issues. There was an awareness of [individual defendant], so there was contemporaneous documentation, records, emails, and such like that --

Mr. Sugden: Objection. Hearsay.

The Court: One moment ... Well, so far he referred to records, emails, and the like but did not tell us what they are. Is that your objection? 

Mr. Sugden: He shouldn't be.

The Court: So I'm going to sustain the objection to having [expert witness] talk about what is in the emails. So why don't I stop you there [expert witness] and have [plaintiff's counsel] follow up. 

Even when the question is not objectionable, trial counsel must be on the lookout for expert witnesses volunteering case-specific hearsay. In that same trial, the plaintiff's attorney sought even more blatantly to have an expert witness relay case-specific facts to the jury. The plaintiff retained a second expert on workplace investigations. But rather than have the expert assume case-specific facts (permitted by Sanchez), the plaintiff's lawyer tried to have the expertrelay case-specific facts (prohibited by Sanchez). See how the trial court sustained the objections, and even explained to the plaintiff's lawyer how to properly frame the question: 

Q Based on our history, experience, and your expert testimony, in your view of any documents or depositions, did you learn that at [Employer] there were individuals who worked part-time in dispatch after [Plaintiff] returned to work in December of 2013?

Mr. Sugden: Objection. Hearsay. 

The Court: Sustained. [Plaintiff's counsel], I will be sustaining objections to ask this witness to tell the jury what he thinks the evidence will show. 

Here is another example: 

Q In your review of any documents or deposition testimony prior to your testimony here today, did you find any evidence that [Plaintiff] requested part-time work after she returned from her maternity leave as an accommodation?

Mr. Sugden: Objection. Hearsay. 

The Court: Sustained. If you want to ask a hypothetical, you may, but as to that question, I'm sustaining.  

Direct Examination: Sanchez and the Resurrection of Hypothetical Questions

The Sanchez court made clear the distinction between general-background hearsay (admissible) and case-specific hearsay (inadmissible). See Sanchez, 63 Cal. 4th at 677. One example the Court used to illustrate this distinction was a hypothetical car accident case. This hypothetical case involved an accident reconstruction expert who would rely on the case-specific fact that there were fifteen-feet skid marks at the scene of the accident. This case-specific fact would be the "matter" the expert relied on to opine that the car leaving those marks was going eighty miles per hour when the brakes were applied. Id. 

The Sanchez court explained that the existence of the fifteen-foot skid would need to be established, not through the expert, but through testimony of a person who measured the marks. Id. The expert witness would then be permitted to testify about (1) how automobile skid marks are left on pavement, (2) that there is a specific equation to estimate speed based on skid mark distance, and (3) that a fifteen-foot skid mark indicates the car was traveling eighty miles per hour. Id.  

With respect to mechanics of how to introduce such evidence, the desired order is as follows: First, call the fact witness who will testify to measuring the fifteen-foot skid mark at the accident scene. Second, call the expert witness. After establishing the foundation of the witness' qualifications, request the expert witness to identify the materials that he relied on to complete his assignment of opining on the speed of the car. Pre-Sanchez, the expert would likely be able to relay the hearsay evidence of the prior witness that the skid mark measured fifteen feet. 

In this example, the expert witness still may be permitted to relay the hearsay evidence because such evidence has already been testified to by the prior witness. Nevertheless, in the event the objection is sustained, you will want to ask hypothetical questions that closely track the testimony of the person who measured the skid mark. For example:

Q Based on your training and experience, are you able to estimate the speed of cars by the length of skid marks at the scene of accidents?

Q Can you explain to the jury how you are able to estimate the speed of cars by the length of skid marks at the scene of an accident? 

Q So for example, if I asked you to assume there was a skid mark of a certain length at the scene of the accident in this case, would you be able to estimate the speed of the car when the brakes were applied? 

Q More specifically, I now want you to assume that there was a skid mark measuring fifteen feet at the scene of the accident. Do you understand? 

Q Assuming there was a fifteen-foot skid mark at the scene of the accident, how fast do you estimate the car was traveling when the brakes were applied? 

With Sanchez resurrecting the implementation of hypothetical questions, lawyers should familiarize themselves with the cases analyzing their use. As an initial matter, each assumed fact in a hypothetical question must be supported by evidence. See Rowe v. Such, 134 Cal. 573, 576 (1901). This does not mean that the assumed facts must be undisputed. See Guardianship of Jacobson, 30 Cal. 2d 312, 324 (1947). Nor does it mean there cannot be minor variances of the assumed facts based on reasonable inferences from the evidence. See e.g., Div. of Labor Law Enforcement v. Gifford, 137 Cal. App. 2d 259, 266 (1955); Sullivan v. City & County of San Francisco, 95 Cal. App. 2d 745, 762 (1950). 

People v. Xue Vang, 52 Cal. 4th 1038 (2011) is an important example where the California Supreme Court examined whether hypothetical questions could too closely track the evidence in the case. Xue Vang was a criminal assault case wherein the prosecution also sought to prove that the assault was committed for the benefit of the Tiny Oriental Crips (TOC), a criminal street gang. Id. at 1041. The prosecution's theory was that the victim of the assault was attacked because either (1) the victim sought to disassociate himself from the TOC, or (2) the victim may have been "checked" because he had heard something he should not have heard. Id. at 1042. 

The prosecution called an expert witness to testify about criminal street gangs. The prosecution asked hypothetical questions on direct examination that closely tracked the evidence in the case. Rather than use the victim's name, the prosecutor referred to a hypothetical involving a "young baby gangster." Id. at 1042-43. And instead of referring to the four defendants by name, the prosecutor gave hypothetical names as "'three baby gangsters and one O.G.,' that is, 'original gangster.'" Id. at 1045. After stating the hypothetical facts, the questions and testimony included the following: 

Q Based on the facts of that hypothetical, do you have an opinion as to whether this particular crime was committed for the benefit of and [in] association with or at the direction of the Tiny Oriental Crips street gang? 

A [It is my opinion that] they [the three baby gangsters and one O.G.] to keep the gang strong because the gang set is only as strong as its weakest member. And that member did something to the TOC gang for him to be victimized in this case. They put him in check. They brought him back in line over some perceived wrong that this individual did to that set....

Q [Do you have] an opinion about whether or not this was a gang-motivated attack?

A [I do.]

Q What is your opinion about the gang motivation behind the attack that has been described in the hypothetical?

A The reason I feel that it was gang motivated is what you told me exactly as far as the fact that this individual, in this hypothetical, is saying that he had been hanging. He had been associating with the documented gang members. He tells me that ... he has been a gang member.... The fact that he was lured out to where he was attacked tells me that that was planned. The fact that it was done in concert with known documented gang members ... tells me that this is a gang-motivated incident. It wasn't about friends fighting among one another.

Id. at 1043. 

The defendant argued that the hypothetical questions were improper because the only apparent differences between the evidence of the case and the facts of the hypothetical scenarios were the names of the parties. Id. at 1045. The Court of Appeal agreed and condemned the questions because they tracked the evidence in a manner that was only "thinly disguised." Id. The California Supreme Court disagreed, and held that the Court of Appeal ruling turned the requirement that hypothetical questions be rooted in facts shown by the evidence on its head:

But the Court of Appeal found these questions were too closely based on the evidence in a manner that was only "thinly disguised." This conclusion transforms the requirement that a hypothetical question be rooted in the evidence into a prohibition—or at least into the confounding rule that the party posing the questions must disguise from the jury the fact it is rooted in evidence—and not "thinly," it appears, but thickly. 

Id. at 1046  

In addition to avoiding hearsay problems, Xue Vang also illustrates how hypothetical questions can be used to have experts opine on ultimate issues in the case which, if the question was expressly tied to the evidence of the case (instead of a closely aligned hypothetical), would be otherwise inadmissible. For example, the Court discussed an earlier case, People v. Killebrew, 103 Cal. App. 4th 644 (2002), wherein an expert opined on his belief of the suspect's (i.e., not a hypothetical person) knowledge and intent during the commission of an alleged crime.

The Xue Vang Court explained that Killebrew must be read to prohibit an expert opining on the knowledge and intent of the specific defendant. But opining on the knowledge and intent of a hypothetical person would be admissible: "It would be incorrect to read Killebrew as barring the questioning of expert witnesses through the use of hypothetical questions regarding hypothetical persons." Xue Vang, 52 Cal. 4th at 1047. 

Finally, the Court explained that prohibiting the expert in Killebrew to offer an opinion on the specific defendant's intent was not inadmissible because it embraced an ultimate issue in the case. Id. at 1048, citing Cal. Evid. Code § 805 ("Testimony 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."). Rather, opinions on the guilt or innocence of a specific defendant are inadmissible because they are of no assistance to the trier of fact; the trier of fact is as competent as the witness to weigh the evidence and draw a conclusion on the issue of guilt. Id., citing People v. Coffman and Marlow, 34 Cal. 4th 1, 77 (2004).  

Direct Examination: The Logistics of Witness Order During Trial 

Turning back to the car skid example discussed in Sanchez, the prior section discussed how the desired order of witnesses was first the fact witness who would testify to measuring the skid mark followed by the expert witness. However, a  common challenge during trial is the logistics of scheduling witnesses. Expert witnesses can have especially limited windows of availability. Accordingly, expert witnesses are sometimes called to testify before the facts they relied on are admitted into evidence. 

It is thus important to know that trial courts have the discretion to permit hypothetical questions incorporating assumptions not yet supported by the evidence if counsel represent that such evidence will be subsequently produced. See Cal. Evid. Code § 403(b) ("[T]he court may admit conditionally the proffered evidence ... subject to evidence of the preliminary fact being supplied later in the course of trial."). But if the supporting evidence is not ultimately received, the objecting party must move to strike the opinion testimony based upon the unsupported hypothetical. See Hyatt v. Sierra Boat, 79 Cal. App. 325, 339 (1978); see also Ault v. International Harvester Co., 13 Cal. 3d 113, 117 (1974) ("When evidence is adduced upon the theory that it will be properly connected, subject to a motion to strike, and that motion is not subsequently urged, a party is deemed to have waived the objection thereto."). 

Direct Examination: Submitting Hypothetical Questions to the Court and Parties in Advance of Testimony

Some authorities suggest that if they intend to use hypothetical questions, the questions should be drafted in advance and circulated to both the court and opposing counsel. See Raoul D. Kennedy & James C. Martin, California Expert Witness Guide, § 13.9 (2d ed Cal. CEB), citing People v. Hayes, 172 Cal. App. 3d 517 (1985). While preparing thoughtful hypothetical questions prior to the expert taking the stand is sound advice, there is no requirement that such questions be presented to your opponent in advance. And without any mandatory requirement, the wisdom of sharing questions with one's opponent should be carefully considered.  

Cross-Examination: The Garbage In, Garbage Out  

Cross-examining expert witnesses can be challenging because, well, they are experts. And they are often professional witnesses. They often have years of experience testifying at deposition and trials, so trying to attack their opinions head-on (i.e., debating substantive issues of the witness' expertise) will often backfire with something like the following: 

Q Well, Mr. Expert Witness, you've just told the jury that plaintiff's reported symptoms are consistent with a diagnosis of anxiety and depression. But sir, isn't it true that plaintiff's symptoms could just as easily be consistent with a thyroid disorder?

A No. Not at all. You are completely wrong, and let me explain why you are wrong... 

And from there, the witnesses will overwhelm the cross-examiner with medical-speak about the differences between depression and thyroid disease. The answer will give the witness an opportunity to become a teacher to the jury (and the cross-examiner). Not only can such questions not prove the intended point, but they can have the unintended consequence of bolstering the credibility of your opponent's expert.

One effective strategy when cross-examining expert witnesses is to attack the materials that form the basis of the expert's opinion or the assumed facts relied on in hypothetical questions. For example, in the employment trial described above, the plaintiff's workplace investigation expert was provided with the plaintiff's deposition transcript, but not another witness' deposition transcript (who contradicted the plaintiff's testimony). The following questions were asked to illustrate two things: (1) the expert was not provided all relevant evidence (i.e., the foundation for his opinions were faulty), and (2) the plaintiff's lawyer cherry-picked information for the expert (i.e., the jury should not only be suspicious of the expert's opinions, but they should be suspicious of the plaintiff's lawyer's tactics): 

Q [Mr. Sugden] ... [I]n terms of the information you received to formulate your opinions, that came from [Plaintiff's lawyer's] office as well as your [re]view of various deposition transcripts that you received from [Plaintiff's lawyer's] office, yes?

A That's some of what I reviewed, yes.

Q And you indicated that among the things that you asked for but did not receive was [third party's] deposition transcript?

A I believe that's the only thing I asked for that I did not receive.

Q Did you ever receive [third party's] deposition transcript?

A No.

Q No, you never received it? 

A Correct, I never received [third party's] deposition transcript?

Q And in your review of [Plaintiff's] deposition, you read that she claimed to make various complaints [about Defendant] to [third party]; correct?

A Yes. 

[What is omitted here are my questions wherein I ask and, where necessary read into the record the plaintiff's testimony, about instances where the plaintiff testified that this third party witness saw various events consistent with the plaintiff's allegations.]

Q Now, among the materials you requested from [Plaintiff's lawyer] was [third party's] deposition transcript; correct?

A Yes.

Q And [Plaintiff's lawyer] told you that [third party's deposition had not been taken in the case?

A In this case.

Q [Plaintiff's lawyer] did not inform you of the fact that [third party witness' deposition] was taken in this case five months prior to your deposition?

A That's not what he said to me.

Q And even after your deposition, you were never given a copy of [third party's] deposition transcript? 

A It wouldn't be appropriate for me to review it after my deposition. 

Q That wasn't my question. My question was [']were you ever corrected of the fact that [third party's] deposition was in fact taken in this case?[']

A No. 

And so it went. Rather than focus on the substance of the expert's expertise, the focus was on the fact that the expert was not provided all relevant materials before forming his opinion. So no matter how qualified the expert may have been, his opinion was based only on the plaintiff's version of events. And making matters worse, the opinion was deprived the opportunity to review another deposition transcript to see whether the plaintiff's testimony was corroborated or contradicted.

The desired result is that the expert's testimony is essentially a push: whether the opinion has any credibility will turn on whether plaintiff's version of events was true or untrue. "Like a house built on sand, the expert's opinion is no better than the facts on which it is based." Kennemur v. State of California, 133 Cal. App. 3d 907, 923 (1982). Put another way: garbage in, garbage out. 

David Sugden is a shareholder at Call & Jensen. He can be reached at [email protected].