State of Arizona v. Hon. bernstein/herman, 237 Ariz. 226

Background

Eleven defendants charged with aggravated DUI had blood tested for BAC by the Scottsdale Crime Laboratory (SCL) using a PerkinElmer Clarus 500 gas chromatograph (the 2003 Instrument).
Defendants moved to exclude BAC evidence under Arizona Rule of Evidence 702, pointing to instrument "data drops," occasional mislabeling, and internal emails expressing staff concern about unresolved malfunctions.
The trial court held a 17-day Daubert-style hearing and found the State satisfied Rule 702(a)–(c) but excluded the BAC results under Rule 702(d), concluding the methodology was not reliably applied given the lab emails and malfunctions.
The court of appeals reversed, finding no showing that successful readings produced by the instrument were unreliable, and ordered admission of the results.
The Arizona Supreme Court granted review to clarify Rule 702(d)’s application and whether application errors require exclusion of expert evidence.

Issues

Issue	State's Argument	Defendants' Argument	Held
Whether trial courts must evaluate an expert’s application of a generally reliable methodology under Ariz. R. Evid. 702(d)	Gatekeeping should consider application but not displace the jury; methodology application challenges are proper for the court to consider	Trial court must exclude when application is flawed because unreliable application undermines admissibility	Trial courts must consider application under Rule 702(d); challenges to application are part of gatekeeping (court affirms gatekeeper role)
Whether SCL’s instrument malfunctions (data drops, mislabeling, emails) rendered defendants’ BAC results inadmissible	The State showed gas chromatography was reliably applied to these particular samples; malfunctions did not prove inaccuracy of the admitted results	Malfunctions and internal concerns undermined confidence in the results and warranted exclusion	The record did not show the malfunctions made these defendants’ results unreliable; exclusion was an abuse of discretion; evidence must be admitted
Standard for excluding expert evidence based on errors in application of a reliable methodology	Exclusion appropriate only when application errors render the underlying results unreliable; otherwise issues go to weight	Errors in application justify exclusion to protect reliability and jury from misleading evidence	Adopts approach that application errors warrant exclusion only if they so infect the procedure or conclusions as to make results unreliable; otherwise admissible and for jury to weigh
Allocation between gatekeeper and jury when application is disputed	Gatekeeper must screen for unreliability but leave borderline credibility/weight issues to jury via adversary testing	Gatekeeper should exclude when there is substantial concern about application	Gatekeeper must evaluate application, but close or non-dispositive application flaws should be tested by adversarial process and jury determines weight/credibility

Key Cases Cited

Daubert v. Merrell Dow Pharm., 509 U.S. 579 (1993) (establishes federal gatekeeping framework for expert admissibility)
In re Paoli R.R. Yard PCB Litig., 35 F.3d 717 (3d Cir. 1994) (exclude only when flaw is large enough that expert lacks good grounds for conclusions)
United States v. Martinez, 3 F.3d 1191 (8th Cir. 1993) (exclude only if deficient application negates reliability of the principle itself)
State v. Langill, 945 A.2d 1 (N.H. 2008) (application errors should not automatically render testimony inadmissible unless they make results unreliable)
State v. Salazar-Mercado, 234 Ariz. 590 (2014) (Arizona precedent on Rule 702 burden and application of expert testimony)
State v. Clemons, 110 Ariz. 555 (1974) (jury’s province to assess weight and credibility of evidence)