State v. Babich, ___ N.C. App. ___, 797 S.E.2d 359 (Mar. 7, 2017)

In this DWI case, the trial court erred by admitting retrograde extrapolation testimony by the State’s expert witness. That expert used the defendant’s 0.07 blood alcohol concentration 1 hour and 45 minutes after the traffic stop to extrapolate that the defendant had a blood alcohol concentration of 0.08 to 0.10 at the time of the stop. To reach this conclusion, the expert assumed that the defendant was in a post-absorptive state at the time of the stop, meaning that alcohol was no longer entering the defendant’s bloodstream and thus her blood alcohol level was declining. The expert conceded that there were no facts to support this assumption. The expert made this assumption not because it was based on any facts in the case, but because her retrograde extrapolation calculations could not be done unless the defendant was in a post-absorptive state. The expert’s testimony was inadmissible under the Daubert standard that applies to Evidence Rule 702. The court added: “Although retrograde extrapolation testimony often will satisfy the Daubert test, in this case the testimony failed Daubert’s ‘fit’ test because the expert’s otherwise reliable analysis was not properly tied to the facts of this particular case.” It explained:

[W]hen an expert witness offers a retrograde extrapolation opinion based on an assumption that the defendant is in a post-absorptive or post-peak state, that assumption must be based on at least some underlying facts to support that assumption. This might come from the defendant’s own statements during the initial stop, from the arresting officer’s observations, from other witnesses, or from circumstantial evidence that offers a plausible timeline for the defendant’s consumption of alcohol.

         When there are at least some facts that can support the expert’s assumption that the defendant is post-peak or post-absorptive, the issue then becomes one of weight and credibility, which is the proper subject for cross-examination or competing expert witness testimony. But where, as here, the expert concedes that her opinion is based entirely on a speculative assumption about the defendant—one not based on any actual facts—that testimony does not satisfy the Daubert “fit” test because the expert’s otherwise reliable analysis is not properly tied to the facts of the case.

The court went on to find that in light of the strength of the State’s evidence that the defendant was appreciably impaired, the error was not prejudicial.