Lead Opinion
OPINION
By the Court,
In this original writ proceeding, we consider the admissibility of retrograde extrapolation evidence to estimate a defendant’s blood alcohol level at a point in time based on a blood sample taken at a later point in time. We conclude that although retrograde extrapolation evidence is relevant in a prosecution for driving under the influence, under certain circumstances such evidence may be unfairly prejudicial and therefore inadmissible. Because the prosecution in this case had to rely on the results from a single blood
FACTS AND PROCEDURAL HISTORY
The State charged real party in interest Bobby Armstrong with driving under the influence causing death and/or substantial bodily harm under two theories of liability: that he (1) was “under the influence of intoxicating liquor” or (2) had “a concentration of alcohol of 0.08 or more in his . . . blood or breath” and did “any act or neglect[ed] any duty imposed by law while driving or in actual physical control” of a vehicle. NRS 484C.430(1) (formerly NRS 484.3795). According to the indictment, Armstrong was driving when his vehicle collided with another vehicle, causing substantial bodily harm to the other driver. The collision occurred at approximately 1:30 in the morning. A single blood sample was taken from Armstrong at 3:51 a.m., more than two hours after the collision. That blood sample had an alcohol level of .18. Armstrong filed a pretrial motion to exclude the blood alcohol test result. He argued that his blood was drawn outside the statutory two-hour window provided in NRS 484C.430(l)(c)
After a lengthy evidentiary hearing involving the conflicting testimony of two expert witnesses, the district court granted Armstrong’s motion in part. The district court excluded retrograde extrapolation as a means of determining Armstrong’s blood alcohol level at the time he was driving and the numerical result of the blood alcohol test but allowed the State to present more generalized
DISCUSSION
A writ of mandamus is available to compel the performance of an act that the law requires as a duty resulting from an office, trust, or station, NRS 34.160, or to control a manifest abuse or arbitrary or capricious exercise of discretion, see Round Hill Gen. Imp. Dist. v. Newman,
The admission or exclusion of evidence rests within the district court’s sound discretion. Thomas v. State,
The evidence at issue in this case involves retrograde extrapolation. Retrograde extrapolation is a “mathematical calculation used to estimate a person’s blood alcohol level at a particular point in time by working backward from the time the blood [sample] was taken.” Com. v. Senior,
Relevance is the first question in determining whether retrograde extrapolation evidence is admissible. See NRS 48.025 (providing that “[a]ll relevant evidence is admissible” unless otherwise excluded by statute or constitutional provision and that “[e]vidence which is not relevant is not admissible”). “ ‘[R]elevant evidence’ means evidence having any tendency to make the existence of any fact that is of consequence to the determination of the action more or less probable than it would be without the evidence.” NRS 48.015. The district court appears to have concluded that retrograde extrapolation evidence had some relevance to the State’s theories that Armstrong was driving under the influence or had a blood alcohol concentration above the legal limit at the time he was
Having determined that retrograde extrapolation evidence is relevant, we turn to the second question in determining whether retrograde extrapolation evidence is admissible: the danger of unfair prejudice. Under NRS 48.035(1), relevant evidence is inadmissible “if its probative value is substantially outweighed by the danger of unfair prejudice.” Because all evidence against a defendant will on some level “prejudice” (i.e., harm) the defense, NRS 48.035(1) focuses on “unfair” prejudice. This court has defined “unfair prejudice” under NRS 48.035 as an appeal to “the emotional and sympathetic tendencies of a jury, rather than the jury’s intellectual ability to evaluate evidence.” Krause Inc. v. Little,
Here, the district court’s concern regarding unfair prejudice centered on the “many unknown variables” in the retrograde extrapolation calculation coupled with the reliance on a single blood sample. The suggestion is that the evidence is of limited probative value given those variables and the single sample, but the evidence itself is likely to move a jury to declare guilt based solely on a reaction to the blood alcohol level and the very real devastation caused by drunk driving rather than proof that the defendant was driving while under the influence or with a prohibited blood alcohol level. We, along with other jurisdictions, share the district court’s concern.
Some jurisdictions have determined that the admissibility of retrograde extrapolation depends on whether enough factors affecting the calculation are known and have expressed concerns with calculations that rely solely on average rates of absorption and excretion. For example, in Mata v. State, the Texas Court of Criminal Appeals provided some guidance by explaining three factors courts should use in evaluating the reliability of retrograde extrapolation:
(a) the length of time between the offense and the test(s) administered; (b) the number of tests given and the length of time between each test; and (c) whether, and if so, to what extent, any individual characteristics of the defendant were known to the expert in providing his extrapolation. These*935 characteristics and behaviors might include, but are not limited to, the person’s weight and gender, the person’s typical drinking pattern and tolerance for alcohol, how much the person had to drink on the day or night in question, what the person drank, the duration of the drinking spree, the time of the last drink, and how much and what the person had to eat either before, during, or after the drinking.
If the State had more than one test, each test a reasonable length of time apart, and the first test were conducted within a reasonable time from the time of the offense, then an expert could potentially create a reliable estimate of the defendant’s [blood alcohol content] with limited knowledge of personal characteristics and behaviors. In contrast, a single test conducted some time after the offense could result in a reliable extrapolation only if the expert had knowledge of many personal characteristics and behaviors of the defendant. Somewhere in the middle might fall a case in which there was a single test a reasonable length of time from the driving, and two or three personal characteristics of the defendant were known to the expert. We cannot and should not determine today the exact blueprint for reliability in every case. Suffice it to say that the factors must be balanced.
Id.; see also Burns v. State,
We agree that achieving a reliable retrograde extrapolation calculation requires consideration of a variety of factors. The following factors are relevant to achieving a sufficiently reliable retrograde extrapolation calculation: (1) gender, (2) weight, (3) age, (4) height, (5) mental state, (6) the type and amount of food in the stomach, (7) type and amount of alcohol consumed, (8) when the last alcoholic drink was consumed, (9) drinking pattern at the relevant time, (10) elapsed time between the first and last drink consumed, (11) time elapsed between the last drink consumed and the blood draw, (12) the number of samples taken, (13) the length of time between the offense and the blood draws, (14) the average alcohol absorption rate, and (15) the average elimination rate. We observe, as the Mata court did, that not every personal fact about the defendant must be known to construct a reliable extrapolation,
Turning to this case, the State and Armstrong presented experts who calculated Armstrong’s estimated blood alcohol level based primarily on factors attributed to the “average” person and various hypothetical situations. The factors used in those calculations included: Armstrong’s admission to the investigating officer at the scene that he drank two beers between 5 p.m. and 10 p.m., records indicating that Armstrong weighed 212 pounds, the time of the accident, the time of the blood draw, and the blood alcohol level in the single sample (.18). There was no evidence presented concerning Armstrong’s age or height, the type and amount of food in his stomach, if any, his regular drinking pattern, or his emotional state after the collision.
Although several of the factors identified above were known, other significant factors were not and, significantly, only one blood draw was obtained. As the Mata court recognized, the significance of personal factors is influenced by the number of blood alcohol tests. “[A] single test conducted some time after the offense could result in a reliable extrapolation only if the expert had knowledge of many personal characteristics and behaviors of the defendant.” Id. at 916. Here, significant personal characteristics, such as the
We are not unmindful of the State’s concerns about prosecuting offenders for driving under the influence, but the State’s accusations that the district court’s order “precludes the state from ever convicting a drunk driver of having a .08 or more at [the] time of driving” and “legalizes driving under the influence of alcohol so long as a chemical test is not done within two hours of driving” go a step too far. The State may present evidence that is relevant and not unfairly prejudicial. NRS 48.025(1); NRS 48.035(1). Although retrograde extrapolation has its place in proving that a defendant was driving under the influence, it also has the potential to encourage a conviction based on an improper basis when the calculation is not sufficiently reliable in a given case. There may be circumstances consistent with this opinion in which a calculation based on the results of a single blood sample is reliable and whose relevance is not substantially outweighed by the danger of unfair prejudice; that is up to the district court to determine on a case-by-case basis. But even when retrograde extrapolation evidence is not admissible, other evidence may establish that a defendant was driving under the influence as prohibited by NRS 484C.430(l)(a). See Sheriff v. Burcham,
Notes
The State did not charge Armstrong with a violation under NRS 484C.430(l)(c).
The State filed its petition in the alternative, seeking relief in mandamus or prohibition. Because prohibition is focused on arresting the proceedings of a district court that is acting in excess of its jurisdiction, NRS 34.320, and the district court here clearly had jurisdiction over the prosecution and to decide evidentiary issues, we conclude that prohibition is not the appropriate vehicle for seeking relief in this matter.
The district court’s order is not entirely clear on this point, but its focus on unfair prejudice indicates that the district court determined that the evidence was relevant since the weighing determination for unfair prejudice presupposes that the evidence is relevant. See NRS 48.035(1) (“Although relevant, evidence is not admissible if its probative value is substantially outweighed by the danger of unfair prejudice . . . .”).
Rule 403 is the federal counterpart to NRS 48.035 and provides: “The court may exclude relevant evidence if its probative value is substantially outweighed by a danger of one or more of the following: unfair prejudice, confusing the issues, misleading the jury, undue delay, wasting time, or needlessly presenting cumulative evidence.”
The district court also excluded the blood alcohol level shown in the test result but allowed the State to present general evidence that there was alcohol in the blood sample, which was relevant to the State’s theory under NRS 484C.430(l)(a). Admitting the specific blood alcohol level in this case, where there was a single blood draw, without extrapolation testimony could encourage a guilty verdict based on similar improper grounds as discussed above.
Dissenting Opinion
The majority’s analysis does not distinguish between the science of retrograde extrapolation and the legal standards by which the admissibility of expert testimony is judged and, as a result, falls into error. Only one toxicologist, Dr. Hiatt, testified at the hearing on Armstrong’s motion to suppress.
The “unknown variables” that led the district court to exclude Armstrong’s test results — variables the majority recasts as “factors” but equally fails to tie to the science — might invite unreliable extrapolation in some cases but, per Dr. Hiatt, this is not such a case. True, there was only one blood draw. If we didn’t know whether Armstrong was in the absorption or the elimination phase when his blood was drawn, that could render the test scientifically indeterminate and the test results inadmissible. Here, however, Dr. Hiatt testified that the known facts, combined with the science of retrograde extrapolation, put Armstrong squarely in the elimination phase when his blood was drawn.
The known facts on which Dr. Hiatt relies are these: (1) Armstrong told the police at the scene that he had been drinking beer but that he stopped drinking at 10 p.m.; (2) the collision occurred
“When a person stops consuming alcohol, his or her body eventually reaches an absorption point, where the body completes absorption of the alcohol he or she has ingested, and enters the elimination phase, where the body is only eliminating alcohol.” United States v. Tsosie,
Once a person completes absorption and enters the elimination phase, blood alcohol levels decline in linear fashion at a rate ranging from .015 to .02 mg/mL/h (Dr. Hiatt) or .01 to .03 mg/mL/h (Mr. Cook). Since Armstrong’s blood alcohol was .18 — more than twice the legal limit — two hours and 21 minutes after the collision and almost six hours after he said he took his last drink, Dr. Hiatt was prepared to opine to a reasonable degree of scientific certainty that Armstrong’s blood level at the time of the collision was at least a .08 which, assuming the other elements of the offense are shown, establishes a violation of NRS 484C.430(l)(b). “[I]f this was a borderline case, I would not feel comfortable making these statements, but this is clearly not a borderline case.” Using Armstrong’s 3:51 a.m. blood alcohol level of .18 and Dr. Hiatt’s .015 elimination rate, and accepting that Armstrong had entered the elimination phase by 1:30 a.m., in fact, yields an approximate blood alcohol level at the time of the collision of .21.
Retrograde extrapolation enjoys “general acceptance in the scientific community,” Shea v. Royal Enterprises, Inc., No. 09 Civ. 8709 (THK),
Nothing approaching these situations obtains here. The admission or exclusion of evidence is unquestionably entrusted to the sound discretion of the district court. See Williams v. Dist. Ct.,
Dr. Hiatt holds a B.A. in chemistry from Occidental College, a Ph.D. in organic chemistry from Yale University, and did significant post-doctoral work in clinical chemistry at the University of California Medical Center in San Francisco. He worked for many years as a toxicologist in Las Vegas before his retirement.
The majority places great emphasis on Mata v. State,
