Alcohol toxicology and retrograde extrapolation expert
Expert class library · Personal injury · Either side
Estimates a person's blood alcohol level at the time of an incident and what signs of intoxication would have been visible, central to dram shop and impaired-driving claims. Courts generally accept retrograde extrapolation as a method but exclude it when the expert assumes facts, such as a post-absorptive state, that the record does not support, and they keep forensic toxicologists from offering medical diagnoses of alcoholism.
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What this expert is retained to answer
- How long after the incident was the blood or breath sample taken, and how many samples were there?
- What facts show the person had finished absorbing alcohol by the time of the incident, rather than being assumed?
- What elimination rate did the expert use, and was the result given as a range rather than a single number?
- Which personal facts, such as weight, food, drinking pattern and when drinking stopped, did the expert actually know?
- Is the toxicologist offering an opinion, such as a diagnosis of alcohol addiction, that belongs to a physician?
Methods
- Retrograde extrapolation
- Widmark formula calculation
- Absorption and elimination phase analysis
- Visible intoxication analysis
- Drink count reconstruction
How the testimony is attacked
- Assumed post-absorptive state. Challengers show the calculation only works if the person had stopped absorbing alcohol and that nothing in the record supports that. In State v. Babich the North Carolina Court of Appeals held the opinion failed the Daubert fit test because the expert conceded she had no facts for that assumption.
- Single late test with few known personal facts. Under the balancing approach Texas courts apply, a single test taken well after the event needs many known personal characteristics. In Veliz v. State the Fourteenth Court of Appeals held retrograde extrapolation testimony unreliable and reversed for a new trial.
- Missing drinking history goes to weight. Proponents answer that gaps about what and when the person drank are for cross-examination. In State v. Barber the Second District of Florida quashed an order excluding the State's toxicologist, holding that such gaps go to weight once the method meets section 90.702.
- Range versus point estimate. Experts who give a range built on published elimination rates fare better than those who give a single number. In State v. Trujillo the Oregon Court of Appeals upheld admission of retrograde extrapolation testimony from an expert who explained why he reported a range.
- Beyond toxicology expertise. Opponents argue that a forensic toxicologist cannot diagnose alcoholism or habitual addiction. In Hayes Robertson Group v. Cherry the Third District of Florida upheld exclusion of a toxicologist's habitual addiction opinion in a dram shop case, while his blood alcohol work had been stipulated.
What the public record shows
A deliberately narrow CourtListener search, ("retrograde extrapolation" OR "blood alcohol") AND toxicolog* AND expert AND (Daubert OR "Rule 702"), returned 85 opinions filed since 2015, as of October 3, 2026; broader searches return more. 5 rulings that show how courts handle this class of testimony:
| Outcome | Case | Court | Why |
|---|---|---|---|
| Excluded | State v. Babich252 N.C. App. 165, 797 S.E.2d 359 | N.C. Ct. App. 2017 | The court held the State's retrograde extrapolation testimony inadmissible under North Carolina's Daubert based Rule 702 because the expert assumed a post-absorptive state without any supporting facts, though it found the error harmless. |
| Excluded | Veliz v. State474 S.W.3d 354 | Tex. App. (Houston [14th Dist.]) 2015 | Applying the reliability factors for retrograde extrapolation under Texas Rule 702, the court held the trial court erred in admitting the State's extrapolation testimony and reversed for a new trial. |
| Limited | Hayes Robertson Group, Inc. v. Cherry260 So. 3d 1126 | Fla. Dist. Ct. App. (3d) 2018 | In a dram shop case, the court held the trial court did not abuse its discretion, under Daubert and section 90.702 or older standards, in excluding a forensic toxicologist's opinion that the driver was habitually addicted to alcohol, a medical diagnosis beyond his expertise. |
| Admitted | State v. Trujillo271 Or. App. 785, 353 P.3d 609 | Or. Ct. App. 2015 | The court upheld admission under Oregon's scientific evidence standard of an expert's retrograde extrapolation testimony that reported blood alcohol as a range based on published elimination rates. |
| Exclusion reversed | State v. BarberNo. 2D22-2036 (Fla. 2d DCA Apr. 14, 2023) | Fla. Dist. Ct. App. (2d) 2023 | Granting certiorari, the court quashed an order excluding the State's toxicologist's retrograde extrapolation testimony, holding that missing facts about drinking and behavior go to weight once the method satisfies section 90.702. |
Each case links to the free opinion text on CourtListener.
Under amended Rule 702
Since December 1, 2023, Rule 702 says expressly that the party offering an expert must show the court it is more likely than not that the testimony meets each requirement: that it rests on sufficient facts or data, uses reliable methods, and reflects a reliable application of those methods to the case. Questions about the basis of an opinion are no longer automatically matters of weight for the jury. For how the circuits have applied the amendment, see the Rule 702 tracker, which follows each court of appeals; for what that means for preparing or attacking this class of expert, see the guide on amended Rule 702.
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Last reviewed October 3, 2026. How this page is built: rulings are found by searching court opinions on CourtListener, and each one is read in the opinion before it is summarised here; outcomes are labelled by what the court did with the expert's testimony. No individual expert is named. This page summarises public decisions for orientation and is not legal advice; read the opinion before relying on any ruling.