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Retrograde Extrapolation in DUI Blood


By Patrick T. Barone, Esq. 

Ask a Question - Free & Confidential!

Retrograde extrapolation is the practice of taking a
known blood alcohol level at a known point in time and
relating it an earlier point in time. In the typical drunk
driving case retrograde extrapolation would be performed to relate back a breath or blood alcohol level
derived from a sample taken well after the driving is
known to have occurred. While it is probably fair to say
that because of the October 2003 amendments to
Michigan's drunk driving laws retrograde is far less
important, prosecutors do still attempt to have their
experts attempt retrograde extrapolation at trial. The
typical way that defense attorneys defend these
attempts is to point out, quite rightly, that the prosecution does not have sufficient information about the
accused, or about their drinking habits prior to the
offense. This defense has met with limited success,
and generally goes to weight rather than admissibility.

Relatively recent changes in Michigan's rules of evidence provide defense attorneys with a new and very
potent weapon against these attempts. However, in
order to fully appreciate the manner in which to raise
this defense, and have any hope of success raising it,
defense counsel must have a thorough knowledge of
the science behind retrograde extrapolation, and of the
Michigan rules of evidence as they relate to scientific

The Science of Retrograde Extrapolation

There are essentially two leading scientists practicing in
this discipline, and they are A. W. Jones and Kurt M.
Dubowski. Each of them has a different opinion as to
when and even if retrograde extrapolation can be done
to any degree of scientific certainty.

The Widmark Formula: In 1932 a Swedish scientist
named E.M.P. Widmark published his research
addressing the issues of alcohol's absorption, distribution and elimination in human subjects. This research
still forms the basis for alcohol calculations performed
in today's courtrooms. Widmark found that because of
alcohol's unique characteristics, certain assumptions
can be made relative to the manner in which a person
will absorb alcohol, how this alcohol will be distributed
throughout the body, and how it will eventually be eliminated. The essential problem with the formula is that
there are individual differences in each of these functions, and scientists differ in their opinions relative to the
amount of certainty that can be assigned to a BAC

arrived at using this formula.

The Dubowski school of thought:

Dubowski's position is best summed up
in his in his 1976 article "Human
Pharmacokinetics of Ethanol. I. Peak
Blood Concentrations and Elimination
in Male and Female Subjects," Alcohol
Technical Reports, Vol. 5, No. 4, 55-63
(1976), where he indicates "speculative retrograde
extrapolation of the BAC to any point prior to an experimentally determined value must be avoided in forensic
practice, or so qualified by stated assumptions that the
exercise becomes pointless." Id. at 61.

In an article that strikes at the very core of the Widmark
formula, Dubowski indicates "[B]reath and blood alcohol time curves are subject to short term fluctuations
from the trend line and other irregulatiries, and often do
not follow the typical Widmark pattern." Dubowski,

Absorption, Distribution and Elimination of
Alcohol: Highway Safety Aspects, Journal of Studies
on Alcohol, Supplement, pg 106 (July 1985).
Throughout this article he embarks on a discussion of
each assumption contained in the Widmark formula,
and describes how these assumptions require nothing
short of guesswork. Regarding alcohol absorption,
Dubowski found that "peak alcohol concentrations
reached after ingestion of idential weight-adjusted does
of alcohol typically vary two to threefold, even in homogeneous experimental subject populations and under
identical experimental conditions. Id. at 100.

Dubowski has similar misgivings relative to the issue of
alcohol elimination. In fact, Dubowski calls into question
a concept that is central to the Widmark formula, i.e.,
that alcohol is eliminated by what is termed "zero order
kinetics." Dubowski is of opinion that this model is
flawed when applied "to at least a significant portion of
the population." Id at 100. Dubowski concludes that
any attempt to determine two points on an elimination
curve has "many obvious shortcomings and limitation
for determining functional blood or breath alcohol
decrease rates." Id. at 101.

Dubowski has this to say relative to the distribution of
alcohol: "[B]ecause alcohol is not uniformly distributed
between the cellular and noncellular components of
blood and because of the relative frequency of hematological abnormalities in the population as well as circadian and other shifts of fluid volumes, use of whole
blood alcohol concentrations further complicates the
physical, chemical and biological factors involve in alcohol distribution and partition. Id. at 102.

Finally, Dubowski's conclusion regarding the feasability
of retrograde extrapolation is that "no forensically valid
forward or backward extrapolation of blood or breath
alcohol concentrations is ordinarily possible in a given
subject and occasion solely on the basis of time and
individual analysis results." Id. at 106.

The Jones school of thought:

A.W. Jones is modern Swedish Toxicologist who has
also researched and written extensively on the issues
of alcohol and traffic safety. It would be fair to say that
Jones is pragmatic in his approach to the subject of retrograde extrapolation. Consequently, it is his opinion
that for forensic purposes, an extrapolated BAC should
be given within a range of value, and that in fairness to
a criminal defendant, the lowest value should be
assigned. Jones describes the problem as follows:
[T]he rate of disappearance of ethanol from the blood
has important ramifications in forensic toxicology as
well as in biomedical alcohol research. It sometimes
happens that the blood alcohol concentration (BAC) at
the time of driving must be estimated from the BAC
existing several hours later, for example, at the time of
obtaining a blood sample. This entails making a back-
estimation or retrograde extrapolation of the BAC. For
this purpose, certain assumptions must be made about
the Pharmacokinetics of ethanol for a given individual.
Jones, Disappearance Rate of Ethanol from the
Blood of Human Subjects: Implications in Forensic
Toxicology, Journal of Forensic Sciences, JFSCA, Vol.
38, No. 1, pg 104 (January 1993).
Jones is not however without reservation on the practice. He states that "[T]he rate of ethanol elimination in
drunk drivers has never been established in an
unequivocal way. Id. at 114. He concludes by indicating that the wide variation in elimination rates "should
be considered in legal proceedings dealing with retrograde estimations and related matters, for example, by
use of the concept of reference intervals from clinical
chemistry. Id. at 115.

It should also be noted that while Jones does stop short
of Dubowski's proclamation that retrograde extrapolation is not forensically feasible, he does call the endeavor a "dubious" practice. Jones, Peak Blood-Ethanol
Concentrations and the Time of its Occurrence

after Rapid Drinking on an Empty Stomach, Journal
of Forensic Sciences, JFSCA, Vol. 36, No. 2, March
1991 at page 337.

The Michigan Rules of Evidence

Davis/Frye Standard: Michigan courts evaluate the
admissibility of novel scientific or medical evidence
based on the "Davis-Frye" Test. This test is derived
from the Michigan Supreme Court case of People v
Davis, 343 Mich. 348 (1955), and the Federal case of
Frye v United States, 293 F 1013 (DC Cir 1923).

Under Davis- Frye a party who wishes to challenge scientific or medical evidence must first establish that it is
novel. Craig v Oakwood Hospital, 249 Mich. App 534
(2002). If a party cannot meet this initial burden of
proof, then a Davis-Frye hearing is not required.

Error! Hyperlink reference not valid. On the other
hand, if the Court is satisfied that the challenged evidence is novel, then an evidentiary hearing is mandatory. The responding party then bears the burden of proof
to show that the evidence has general acceptance in
the scientific or medical community. At least ostensibly
the ultimate issue is the reliability of the proffered evidence. People v Beckley, 434 Mich. 691 (1990).

A factor of significance to bear, and one that ought to
always be raised with these types of evidence issues,
is that in making its determination, the Court may only
consider the testimony of impartial experts whose livelihoods are not intimately connected with the evidence in
issue. Anton v State Farm Mutual Automobile Insurance
Co, 238 Mich. App 673 (2000). Also, Michigan Courts
appear to be trending toward a focus on the reliability of
the methodology rather than a determination that the
reliability of the principle or technique is reliable. Id.

MRE 702: In Addition to the Davis-Frye, Michigan
Courts are also may require an analysis based on MRE
702, which provides: "If the court determines that recognized scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an
opinion or otherwise." While there is at least one opinion that suggests that novel scientific evidence may be
evaluated based only on MRE 702 [ Nelson v American
Sterilizer Co, 223 Mich. App 485 (1997)], however most
published cases suggest that it is appropriate for the
trial courts to use both standards in evaluating novel
scientific evidence.

Under MRE 702 the focus should be whether the novel 
scientific evidence relies on proper scientific methodology and principles. At the evidentiary hearing, make the
expert provide support for his opinion, then ask the
court to determine if his supporting evidence is independent and objective and whether or not the principle
or technique is found in recognized scientific and/or
medical literature.

[Like the Daubert standard discussed below] an evidence challenge based on MRE 702 will cause the
Court to consider whether the principle or technique
involved or challenged is "generally accepted as reliable within the relevant scientific or medical community." This standard makes the issue of how "novel" the
evidence might be is much less a focus so long as a
foundation for trustworthiness is reached. If such a
foundation is presented to the Court, then one may
argue that the expert testimony is admissible no matter
how novel.

The Recently Amended MRE 703: MRE 703 was
amended on March 25, 2003, and the changes become
effective beginning on September 1, 2003. These
changes are significant, and may also have an impact
on the admissibility of the DRE's opinion, but only if the
Court first determines that the police officer is providing
an "expert" rather than a "lay" opinion. The rule provides: "The facts or data in the particular case upon
which an expert bases an opinion or inference may be
those perceived by or made known to the expert at or
before the hearing. The court may require that underlying facts or data essential to an opinion or inference be
in evidence."

If the rule applies, then it is probably safe to assume
that the "facts" upon which the witness bases his opinion will be admitted into evidence. It is far less clear
that the "data" upon which he bases his opinion will be
admitted into evidence.

However, the Michigan Advisory Committee Report,
August 2000, at page 12 indicates "in the same vein,
we emphasize that the facts or data that must be in evidence to support an expert opinion are the facts or data
'in the particular case,' as the rule states. As are perhaps obvious, the rule is not intended to require independent proof of the literature, studies, experiments,
etc. that qualify a witness as an expert in the first

The Daubert/Kumho Tire Standard: Two cases that
were decided in the 1990's by the United States
Supreme Court have had a significant impact on the
rules of evidence as they apply to expert testimony, at
least at the Federal Level. These cases are Daubert v.
Merrill Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993)
and Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137

Daubert required trial judges to become "gatekeepers"
of scientific evidence and to decide whether expert testimony will assist the trier of fact, as well as whether the
proffered testimony amounts to scientific knowledge.
Based on Daubert, trial judges are directed to apply a
non-definitive "checklist" in reaching this determination.
The factors set forth in Daubert include the following:

(a) Whether the proposition is testable; (b) Whether the
proposition has in fact been tested; c) Whether the
proposition has been subjected to peer review and publication; (d) Whether the methodology or technique has
a known or potential error rate; (e) Whether there are
standards for using the technique, and; (f) Whether the
methodology is generally accepted.
In Kumho Tire, the Supreme Court held that the admissibility of expert testimony that is based on technical or
specialized knowledge should also be subjected to the
analysis set forth in Daubert. The Court also reaffirmed
that the Daubert factors are not restrictive, but rather
are flexible and are to be applied on a case-by-case
basis. Kumho Tire has had a significant impact on so-
called "soft science" including, among other things,

Using This Information to Keep Retrograde
Extrapolation Out of Evidence

Because there are essentially two schools of thought on
the issue of retrograde, whenever defense counsel is
confronted with this evidence, they should move to
keep it out on the basis that its use is not "generally
accepted in the scientific community." Of course the
prosecution will respond that this type of evidence has
been accepted in the Michigan courts for many years,
and that as a scientific principle retrograde extrapolation is accepted by the scientific community. While true
to an extent, both Jones and Dubowski have misgivings
relative to the scientific reliability of the practice, particularly when it is often the case that very little is actually
known about a motorist other than their gender and
weight. Also, this practice has never been subjected to
the increased scrutiny afforded by recent changes in
the law. Good advocacy suggests that a challenge to
this practice is warranted on this basis along.

[Editor's Note: Patrick T. Barone is a principal in the Barone
Defense Firm, whose practice is limited exclusively to defending the
drunk driving accused. Mr. Barone has published several articles
on trial practice and drunk driving defense tactics, is a frequent lecturer on these topics, and he has also appeared on television and in
newspapers as a recognized drunk driving defense expert.
Additionally, Mr. Barone has been certified as an instructor and
practitioner of the Standardized Field Sobriety Tests in accordance
with the standards set forth by the International Association of
Chiefs of Police (IACP) and the National Highway Traffic Safety
Administration (NHTSA). He has also been certified as competent
by the manufacturer of the DataMaster to operate, perform essential
diagnostic verifications and calibration checks on their machine. Mr.
Barone is sustaining member of the National College for DUI
defense, a member of the National Association for Criminal Defense
Attorneys, The Criminal Defense Attorneys for Michigan, and the
Criminal Law Section of the State Bar of Michigan.]

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