Expert Witness Blog
Defendant appealed her conviction of habitual impaired driving, arguing that the lower court erred when it allowed the state’s expert opinion on retrograde extrapolation. The court concluded that the lower court did err, but this did not prejudice the outcome of the case.
Facts: This case (State of North Carolina v. Lori Lee Babich – Court of Appeals of North Carolina – March 7th, 2017) involves an appeal of defendant’s (Babich) conviction for habitual impaired driving. The appeal involves the lower court’s admission of retrograde extrapolation testimony by the state’s chemistry expert witness, Bethany Pridgen.
Pridgen’s testimony concluded that Babich’s BAC (blood alcohol concentration) was .08 to .10 at the time of her stop by using the BAC level taken one hour and forty-five minutes after the traffic stop. This is called retrograde extrapolation. Pridgen assumed that Babich was in a post-absorptive state at the time of the stop. A post-absorptive state means that alcohol was no longer entering Babich’s bloodstream and, thus, her BAC was declining. Babich appeals her conviction based on this testimony that was allowed by the trial court.
Discussion: Babich argues that the retrograde extrapolation performed by Pridgen was inadmissible because it was not based on sufficient facts or data. To be sure, Babich does not argue that all retrograde extrapolation expert testimony is inadmissible. She does argue that since Pridgen assumed that she was in a post-absorptive state at the time of the stop, Pridgen’s testimony should have been excluded.
Pridgen acknowledged that there are many factors that could impact whether or not someone is in a post-absorptive state, including when alcohol was last ingested and if the person consumed any food that could delay the time it takes for the alcohol to be absorbed into the bloodstream. Pridgen also admitted that she did not have any factual evidence from the case that would prove that Babich was in a post-absorptive state. Pridgen stated that Babish was in a post-absorptive state as the retrograde extrapolation calculations would not work is she wasn’t.
The court did not have jurisdictional precedent on this issue, so they looked in other courts and found that the majority of the courts concluded that this type of evidence does not satisfy the criteria under Daubert.
They point to a similar New Mexico Supreme Court case (State v. Downey), where the court opined that the expert’s testimony could not satisfy the “fit” test because the expert did not sufficiently reliable underlying facts to apply to his methodology. The court then opined that retrograde extrapolation could be admissible if the expert did not have to assume that the defendant stopped drinking prior to the collision and was in a post-absorptive state.
The current court agreed with the New Mexico Supreme Court by opining that when an expert offers testimony using retrograde extrapolation based on an assumption that the defendant is in a post-absorptive state, that assumption must be based on underlying facts to support that assumption.
Conclusion: The court in this case opined that the lower court erred when it allowed the expert’s retrograde extrapolation theory. However, the court further opined that this error did not prejudice Babich. Thus, the conviction was upheld.