According to the indictment, the defendant (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(1)(c) FN1 and that the test was inadmissible because only one blood sample was obtained. He further argued that the retrograde extrapolation that the State would have to use to determine his blood alcohol level at the time he was driving was unreliable and therefore irrelevant and unfairly prejudicial. The State opposed the motion, arguing that retrograde extrapolation was not required to determine Armstrong's blood alcohol level at the time of the collision because his alcohol level was sufficiently high that a jury could determine that it was above .08 while he was driving, but even if the State were required to do so, any variables in the retrograde extrapolation go to the weight of that evidence rather than its admissibility. The State also argued that the blood alcohol test was admissible to show that Armstrong was driving under the influence of intoxicating liquor. 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 evidence that the blood test showed the presence of alcohol.
"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, 433 Mass. 453, 744 N.E.2d 614, 619 (Mass.2001). The calculation requires information regarding the rates at which alcohol is absorbed and excreted. Those rates can vary based on a number of factors, including: the amount of time between a person's last drink and the blood test, the amount and type of alcohol consumed, the time period over which alcohol was consumed, and personal characteristics such as age, weight, alcohol tolerance, and food intake. See Mata v. State, 46 S.W.3d 902, 915–16 (Tex.Crim.App.2001), overruled on other grounds by Bagheri v. State, 87 S.W.3d 657, 660–61 (Tex.App.2002)."
The State then filed a petition for a writ of mandamus against the judge, seeking to force the judge to admit the retrograde evidence. On appeal, the Supreme Court of Nevada affirmed, finding that even though retrograde extrapolation evidence was relevant, there was a danger of unfair prejudice.
"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 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.
46 S.W.3d 902, 916 (Tex.Crim.App.2001), overruled on other grounds by Bagheri v. State, 87 S.W.Sd 657, 660–61 (Tex.App.2002). The court declined to design an “exact blueprint” for all cases and recognized that not every personal fact about the defendant must be known to construct a reliable extrapolation—otherwise “no valid extrapolation could ever occur without the defendant's cooperation, since a number of facts known only to the defendant are essential to the process.” Id. at 916–17. The court also indicated that the significance of those personal factors is influenced by the number of blood alcohol samples obtained and the time between multiple samples:
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, 298 S.W.3d 697, 702 (Tex.App.2009) (concluding that expert's testimony was unreliable due to expert's admission that “he knew none of the factors required by Mata when only a single test is available” and because testimony was unreliable, it was irrelevant and “its probative value was greatly outweighed by its prejudicial effect”); accord Com. v. Petrovich, 538 Pa. 369, 648 A.2d 771, 773 (Pa.1994) (upholding trial court's conclusion that retrograde extrapolation expert's testimony was incomplete and elicited “an expert opinion which is necessarily based upon average dissipation rates, average absorption rates, and the alcohol content of the average drink” (internal quotations omitted)). See generally Kimberly S. Keller, Sobering Up Daubert: Recent Issues Arising in Alcohol–Related Expert Testimony, 46 S. Tex. L.Rev. 111, 122–29 (2004) (discussing concern in scientific community over the use of retrograde extrapolation calculations that do not employ factors that affect individual absorption and elimination rates, including (1) the type and amount of food in the stomach, (2) gender, (3) weight, (4) age, (5) mental state, (6) drinking pattern at the relevant time, (7) type and amount of beverage consumed, and (8) elapsed time between the first and last drink taken).
The Court wrote:
"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, 46 S.W.3d at 916–17, but rather those factors must be balanced."
"[T]he 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.
Concluding, the Court stated:
"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 type and amount of food, if any, in Armstrong's stomach—a factor that Armstrong's expert testified was the most important and the State's expert acknowledged significantly affects alcohol absorption—were unknown. And the single blood draw makes it difficult to determine whether Armstrong was absorbing or eliminating alcohol at the time of the blood draw. The admission of retrograde extrapolation evidence when a single blood draw was taken more than two hours after the accident and the extrapolation calculation is insufficiently tethered to individual factors necessary to achieve a reliable calculation potentially invites the jury to determine Armstrong's guilt based on emotion or an improper ground—that the defendant had a high blood alcohol level several hours later—rather than a meaningful evaluation of the evidence. Thus, although relevant, the probative value of the extrapolation evidence could be sufficiently outweighed by this danger of unfair prejudice to preclude its admission.FN5 Under the circumstances presented, we cannot say that the district court manifestly abused or arbitrarily or capriciously exercised its discretion, that is, applied a clearly erroneous interpretation of the law or one not based on reason or contrary to the evidence or established rules of law.