Lay and Expert Opinion Testimony (Daubert and California Kelly/Sargon)

A lay witness may offer opinions only when they are (a) rationally based on her own perception, (b) helpful to a clear understanding of her testimony or to determining a fact in issue, and (c) NOT based on scientific, technical, or other specialized knowledge within the scope of FRE 702. Classic permissible lay opinions: speed of a car, intoxication, emotional state, identity of a familiar voice or handwriting, that a substance smelled like gasoline. The 2000 amendment added clause (c) precisely to stop parties from smuggling expert testimony in through a lay witness.

Expert testimony under FRE 702 requires a qualified witness AND a reliable basis. After the December 2023 amendment, FRE 702 makes explicit that the proponent must show, by a preponderance, that each requirement is met and that the opinion reflects a reliable application of the methodology — courts may no longer treat shaky application as merely going to weight.

Daubert v. Merrell Dow Pharmaceuticals (1993) interpreted FRE 702 to require the trial judge to act as a GATEKEEPER who screens scientific testimony for relevance and reliability. Non-exclusive factors: (1) whether the theory or technique can be and has been tested; (2) whether it has been subjected to peer review and publication; (3) the known or potential rate of error and existence of standards controlling its operation; and (4) the degree of acceptance within the relevant scientific community.

General Electric v. Joiner (abuse-of-discretion review) and Kumho Tire v. Carmichael (gatekeeping extends to technical and other specialized — not just scientific — testimony) complete the trilogy. FRE 703 governs the BASIS: an expert may base an opinion on facts the expert has been made aware of or personally observed, and those underlying facts need NOT themselves be admissible if experts in the field would reasonably rely on them; but if the data are inadmissible, the proponent may disclose them to the jury only if their probative value in helping evaluate the opinion substantially outweighs their prejudicial effect.

FRE 704(a) abolishes the old common-law bar: an opinion is not objectionable merely because it embraces an ultimate issue (an expert may opine that a product was defective, or a lay witness that the testator 'didn't know what he was doing'). The single exception is FRE 704(b): in a criminal case, an expert witness may NOT state an opinion about whether the DEFENDANT did or did not have a mental state or condition that is an element of the crime or a defense — that ultimate conclusion is reserved for the trier of fact.

The expert may describe the defendant's mental condition generally but not opine that he 'lacked the intent to kill.' FRE 705 permits an expert to state an opinion and give reasons WITHOUT first testifying to the underlying facts, though the expert may be required to disclose them on cross-examination.

Qualifying an expert under FRE 702 is liberal: a witness may be qualified by knowledge, skill, experience, training, OR education, so a tradesperson with decades of hands-on experience can be qualified even without formal credentials, and the absence of a particular degree goes to weight, not admissibility.

Once qualified, the expert's reliability is screened by the Daubert/Kumho gatekeeping inquiry; after the December 2023 amendment, FRE 702 makes the proponent's preponderance burden explicit and directs courts to treat an unreliable APPLICATION of a sound methodology as an admissibility defect, not merely a jury-weight question — reversing the lax 'shaky but admissible' formulations some courts had adopted.

The basis of opinion under FRE 703 creates a recurring Confrontation problem in criminal cases: an expert may rely on inadmissible facts that experts in the field reasonably rely upon, but disclosing those facts to the jury is permitted only when their probative value in helping the jury evaluate the opinion substantially outweighs prejudice (a reverse-403 disclosure test), and Williams v. Illinois and its progeny warn that an expert cannot become a conduit for testimonial hearsay (a non-testifying analyst's report) offered for its truth against the accused.

California's People v. Sanchez (2016) addresses this directly, holding that an expert may state general background knowledge but may NOT relate CASE-SPECIFIC hearsay as 'basis' evidence unless it is independently admissible — a stricter line than the federal practice. Work two hypotheticals. First: in a federal products case, a metallurgist testifies that a bracket failed from hydrogen embrittlement, relying on lab reports she did not personally generate.

Under FRE 703 her reliance is proper if metallurgists reasonably rely on such reports; the reports themselves come in only if the reverse-403 disclosure test is met, and she may answer a hypothetical question incorporating assumed facts under FRE 705 without first reciting every datum. Second: in a California criminal gang prosecution, a gang expert wants to recount specific prior offenses of the defendant's associates drawn from police reports to support a 'gang membership' opinion.

Sanchez bars relating those case-specific hearsay facts as basis testimony unless independently admitted, and the Confrontation Clause (Crawford) independently bars testimonial portions — so the disciplined answer separates admissible general expertise from inadmissible case-specific hearsay. Finally, for NOVEL scientific techniques California applies People v. Kelly's general-acceptance test to the METHOD (not the Daubert reliability factors), while Sargon polices the expert's reasoning for speculation and analytical gaps under CEC 801(b)-802, and People v. Collins cautions against misleading mathematical-probability proof.

Expert Admissibility: Federal vs. California

California has NOT adopted Daubert. For NEW scientific techniques, People v. Kelly (the California version of Frye) requires the proponent to show (1) the method is generally accepted as reliable in the relevant scientific community, (2) the witness is properly qualified, and (3) correct scientific procedures were used. Kelly governs the METHOD's reliability, not the expert's general reasoning. Sargon Enterprises v. USC (2012) then added Daubert-flavored GATEKEEPING under CEC 801(b) and 802: a trial court may exclude expert opinion that is speculative, based on assumptions without evidentiary support, or built on a reasoning gap.

People v. Sanchez (2016) limits an expert from relating CASE-SPECIFIC hearsay as 'basis' testimony when it is offered for its truth (a Confrontation Clause concern in criminal cases). And People v. Collins still warns against misleading mathematical-probability testimony. On a CA essay involving novel forensic science, lead with Kelly general acceptance; for a damages or reasoning challenge, apply Sargon.