Your blood-alcohol concentration level (BAC) is below the
.08 percent legal limit at the time you provide a breath
or blood test at the jail or police station. Will you still
be prosecuted?
Or your BAC is lower at the time of that required implied
consent test than it was at the time of a roadside breath
(preliminary alcohol screening aka PAS) test.
You wonder how your true BAC can be proven at time of driving
based on a test done later.
It’s a definite problem. One can try to guess what
the true BAC was in a San Diego DUI case by projecting backwards,
using average alcohol absorption and elimination rates,
but it’s only an inaccurate guess based on assumptions.
It's called "retrograde extrapolation" —
a pretty name for trying to guess backwards. The San Diego
DUI prosecutor in a San Diego DUI trial often offers BAC
test evidence guessing one's BAC...back to the time of driving.
The blood-alcohol level at the time of a San Diego DUI chemical
test is not relevant to the San Diego DUI charge. The San
Diego DUI prosecutor therefore attempts offer evidence to
show what the BAC was when the San Diego DUI arrestee was
actually driving.
This is commonly done by “extrapolating” backward
- i.e. computing the earlier blood-alcohol level by estimating
how much alcohol had been eliminated or “burned off”
in the period between San Diego driving and DUI testing.
But retrograde extrapolation requires two assumptions:
(1) The San Diego DUI arrestee's blood-alcohol level was
declining; and
(2) The San Diego DUI arrestee's the rate of elimination
is known.
This second assumption further involves the San Diego DUI
prosecution lab employee's (aka expert's) assumption that
the “burn-off” rate was .015 percent per hour
(sometimes the assumed rate is .02 percent).
Over the San Diego DUI Defense Attorney's objection, how
does the San Diego DUI prosecution know that the San Diego
DUI arrestee was eliminating (assuming he or she was eliminating
rather than still absorbing) at that rate and not at .005
percent, .3 percent or some other possible scientific rate?!
Quite simply, the San Diego DUI prosecution does not know.
The San Diego DUI prosecution laboratory employee merely
assumes that the San Diego DUI arrestee was eliminating
and that he or she eliminated at the average rate.
The problem is that everyone has a different metabolism,
and even a given person will metabolize alcohol at different
rates depending on many variables.
In one important study, researchers found a wide range of
metabolism rates: some individuals can absorb alcohol and
reach peak blood-alcohol levels ten times faster than others.
(Kurt Dubowski, “Absorption, Distribution and Elimination
of Alcohol: Highway Safety Aspects”, Journal on Studies
of Alcohol (July 1985)).
As a result, scientists have concluded that the practice
of estimating earlier BAC levels in DUI cases is highly
inaccurate and should be discouraged.
From the recognized expert in the field, Professor Dubowski
of the University of Oklahoma:
It is unusual for enough reliable information to be available
in a given case to permit a meaningful and fair value to
be obtained by retrograde extrapolation. If attempted, it
must be based on assumptions of uncertain validity, or the
answer must be given in terms of a range of possible values
so wide that it is rarely of any use. If retrograde extrapolation
of a blood concentration is based on a breath analysis the
difficulty is compounded.” 21(1) Journal of Forensic
Sciences 9 (Jan. 1976).
“[T]he practice of making back estimation of a person’s
BAC is inevitably a controversial issue in DUI litigation
and should be avoided whenever possible.”
A.W. Jones & Barry K. Logan, Drug Abuse Handbook 1012.
Reprinted in “Forensic Alcohol Supervisor Course”
California Criminalistics Institute – California department
of Justice Hosted by OC Crime Lab 2000
“Making back extrapolations of BAC is not recommended
because of the wide variations in absorption, distribution,
and elimination patterns of ethanol both within and between
different individuals.” Id. at 347
Citing: Allanowai et. al. Ethanol Kinetics – Extent
of Error in Back Extrapolation Procedures. 34 Br. J Clin
Pharmacology 316 (1992); Lewis, Back Calculation of Blood
Alcohol Concentrations 295 Br. Med J 800 (1987)
“This raises the issue of retrograde extrapolation
and there are well-known problems and pitfalls associated
with this practice.”
Jones, Status of Alcohol Absorption Among Drinking Drivers,
14 Journal of Analytical Toxicology (1990)
“Retrograde Extrapolation – A Dubious Practice”
A.W. Jones, Medical Conditions and DWI/DUI Challenges,
NACDL 9th Annual Seminar (2005)
Dr. Kurt Dubowski (Department of Medicine & Toxicology
Laboratories University of Oklahoma)
“It is unusual for enough reliable information to
be available in a given case to permit a meaningful and
fair value to be obtained by retrograde extrapolation. If
attempted, it must be based on assumptions of uncertain
validity, or the answers must be given in terms of a range
of possible values so wide that it is rarely of any use.
If retrograde extrapolation of a blood alcohol concentration
is based on a breath analysis the difficulty is compounded.”
Mason and Dubowski, Breath- Alcohol Analysis: Uses, Methods,
and Some forensic Problems – Review and Opinion 21
J. Of Forensic Sciences 29.
Reprinted in “Forensic Alcohol Supervisor Course”
California Criminalistics Institute – California Department
of Justice Hosted by OC Crime Lab 1998
“Finally, 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”
Dubowski, Absorption, Distribution and Elimination of Alcohol:
Highway Safety Aspects, 10 Journal of Studies on Alcohol
98, 106 (1985)
Reprinted in “Forensic Alcohol Supervisor Course”
California Criminalistics Institute – California Department
of Justice Hosted by OC Crime Lab 1998
“Extrapolation of a later alcohol test result to
the time of the alleged offense is always of uncertain validity
and therefore forensically unacceptable”
Dubowski, Absorption, Distribution and Elimination of Alcohol:
Highway Safety Aspects, 10 Journal of Studies on Alcohol
98, 106 (1985)
Reprinted in “Forensic Alcohol Supervisor Course”
California Criminalistics Institute – California Department
of Justice Hosted by OC Crime Lab 1998
DO NOT USE RETROGRADE EXTRAPOLATION
(7 REASONS)
According to Dr. Dubowski, the existing information on blood
alcohol and breath alcohol versus time curves, the following
conclusions can be reached:
1. Not all blood and breath alcohol curves follow the Widmark
patterns nor is the elimination necessarily linear.
2. Alcohol absorption is not always complete within 60 to
90 minutes, as often claimed.
3. The peak alcohol concentration cannot be validly predicted
or established in an individual instance without frequent
and timely measurements of alcohol concentrations.
4. It is not possible to establish whether an individual
is in the absorption or elimination phase, or to establish
the mean overall rate of alcohol elimination from the blood
or breath, from the results of two consecutive blood or
breath alcohol measurements, however timed.
5. Significantly large short-term fluctuations occur in
some subjects and result in marked positive and negative
departures from the alcohol concentration trend line.
6. Short-term, marked oscillation of the blood or breath
alcohol concentration can occur at various points of the
curve, resulting in repeated excursions of the alcohol concentration
above and below a given concentration (such as 80 or 100
mg/dl) within a few minutes or for hours.
7. 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.
Absorption, Distribution and Elimination of Alcohol: Highway
Safety Aspects, Journal of Studies on Alcohol Supplement
No. 10, July 1985, Dr. Kurt M. Dubowski, Department of Medicine,
and Toxicology Laboratories, The University of Oklahoma
Health Sciences Center, Oklahoma City, Oklahoma 73190.
DR. DUBOWSKI found that elapsed time from end of alcohol
intake to peak blood alcohol concentration varying from
14 to 138 (2hrs. 18 min) minutes, a nearly 10-fold variation.
Equations for blood alcohol concentrations require knowledge
of many various factors (times of drinking, quantities of
alcohol, food, weight, etc.). As such, numbers can be worked
in the direction of the Prosecution or the Defense.
Most San Diego DUI Prosecution "experts" make
wrong or questionable assumptions (for example, they usually
assume the subject has an "average" rate of alcohol
elimination and they usually assume absorption is complete)
and, therefore, they come up with questionable, unreliable
estimates that should not be allowed into evidence.
If all complete and accurate information is known (San Diego
DUI Prosecution lab employees usually do NOT know), BAC
calculations may be estimated but only with broad ranges
of absorption times and a range of elimination rates. The
calculations MUST NOT ASSUME SOME AVERAGE VALUES AND MUST
NOT ASSUME COMPLETE ABSORPTION. Retrograde extrapolation
without this type of information and without ranges of values
is junk science. Normally, the State does not have the required
information to perform retrograde extrapolation correctly.
Q. for San Diego DUI Prosecutor: You have a San Diego DUI
breath test machine reading of .09% an hour or two after
the driving. Scientists say you cannot accurately project
that BAC back to the time of driving. If the BAC was rising,
it could have been a .07% or even lower. Problem. What to
do?
A. You attempt to use California legislation saying that
the blood-alcohol when tested is presumed the same as it
was when driving.
(But that is not true because BAC constantly changes as
alcohol is metabolized.)
Q. How can one legally presume what we know is incorrect?
A. One can never really know.
(But it makes the San Diego DUI prosecutor’s job easier.)
Despite a Presumption of Innocence, make the San Diego DUI
defendant try to prove what his or her BAC was an hour or
two earlier. California somehow says one's BAC was the same
3 hours earlier — unless one can prove it was not!
Here is California’s DUI law:
"In any prosecution under this subdivision, it is a
rebuttable presumption that the person had 0.08% or more,
by weight, of alcohol in his or her blood at the time of
driving the vehicle if the person had 0.08 percent, by weight,
of alcohol in his or her blood at the time of performance
of a chemical test within three hours after the driving”.
(Vehicle Code sec. 23152(b))
POINTS & AUTHORITIES TO EXCLUDE RETROGRADE EXTRAPOLATION
AS IT DOES NOT MEET THE DAUBERT “GATEKEEPER”
STANDARD (FEDERAL RULES OF EVIDENCE, RULE 702)
In order for scientific evidence to be admissible, it must
satisfy the Daubert Standard. Under Daubert, courts must
engage in a difficult, two-part analysis. First, a court
must determine nothing less than whether the expert’
testimony reflects scientific knowledge, whether their findings
are derived by the scientific method, and whether their
work product amounts to good science. Second, a court must
ensure that the proposed expert testimony is relevant to
the task at hand, i.e., that it logically advances a material
aspect of the proposing party’s case. The United States
Supreme Court refers to this second prong of the analysis
as the “fit” requirement. (Daubert v. Merill
Dow Pharmaceuticals 43 F.3rd 1311; (1995) Judges perform
a gatekeeping role; to do so they must satisfy themselves
that scientific evidence meets a certain standard of reliability
before it is admitted. An expert’s bald assurance
of validity is not enough. Rather, a party presenting an
expert must show that the expert’s findings are based
on sound science, and requires some objective, independent
validation of an expert’s methodology. (Daubert)
Under Federal Rules of Evidence, Rule 702, the court’s
responsibility is to determine whether proffered scientific
evidence is sufficiently reliable and relevant to assist
the jury. “The proponent of the scientific evidence
must demonstrate by clear and convincing evidence that the
evidence is reliable. This is accomplished by showing the
validity of the underlying scientific theory, the validity
of the technique applying the theory, and the proper application
of the technique on the occasion in question” (Mata
v. The State of Texas, 46 S.W.3rd 902 (Tex.Cr.App. 2001):
Factors that may affect reliability include, but are not
limited to, the following: (1) the extent to which the underlying
scientific theory and technique are accepted as valid by
the relevant scientific community, if such a community can
be ascertained; (2) the testifying expert’s qualifications;
(3) the existence of literature supporting or rejecting
the underlying scientific theory or technique; (4) the technique’s
potential rate of error; (5) the availability of other experts
to test and evaluate the technique; (6) the clarity with
which the underlying scientific theory and technique can
be explained to the court; and (7) the experience and skill
of the person who applied the technique on the occasion
in question.
In Mata, the court analyzes the science of “retrograde
extrapolation” - the computation back in time of the
blood-alcohol level. The estimation of the level of the
blood-alcohol at the time of driving based on the result
of a test taken some time later. The court determined that
multiple tests will increase the ability by an expert to
plot a subject’s BAC curve, a test nearer in time
to the time of the alleged offense increases the ability
to determine subject’s offense-time BAC, and the more
personal information known to the subject increases the
reliability of an extrapolation. In determining the reliability
of retrograde extrapolation, the court should consider:
(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 whether, and if so, to what
extent, any individual characteristics of the defendant
are 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, and 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 that person had to eat either before, during,
or after the drinking.
The court went on to recognize that the expert does not
need to know every single personal fact about the defendant
in order to produce an extrapolation with the appropriate
level of reliability. 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 BAC 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.
In the present case, the State of California intends to
extrapolate back to prove this San Diego DUI arrestee was
under the influence while driving. There are times of driving,
PAS tests and implied consent breath tests. Because of the
remoteness of the alleged driving and the test results,
an expert must have knowledge of many personal characteristics
and behaviors of defendant in order for the retrograde extrapolation
to be reliable.
From defendant's driver’s license information, an
"expert" can attempt to obtain his height and
weight (at one time), but nowhere in the police report does
it state defendant's typical drinking pattern and tolerance
to alcohol, and how much and what he had to eat either before,
during, or after the drinking. The only information available
is in the police report which states that defendant admitted
to having drinks. This clearly is not enough to make a reliable
extrapolation.
RETROGRADE EXTRAPOLATION DOES NOT MEET THE KELLY/FRYE “GENERAL
ACCEPTANCE” TEST
Under the Kelly/Frye rule, a new scientific technique must
be sufficiently established to have gained general acceptance
in the particular field in which it belongs, in order to
be admissible in evidence. The proponent of the evidence
bears the burden of proving a consensus of opinion and must
establish (1) the reliability of the method, usually by
expert testimony; (2) the qualifications of the witness
providing the testimony; and (3) that correct scientific
procedures were used in the particular case. The expert
witness must possess academic and professional credentials
that permit him to understand the scientific principles
involved and any differing viewpoints regarding reliability.
The witness must also be impartial -- not so personally
invested in establishing the technique's acceptance that
he might not be objective about disagreements within the
relevant scientific community. People v. Morris, 199 Cal.
App. 3rd 377, (1988).
RETROGRADE EXTRAPOLATION IS MORE PREJUDICIAL THAN PROBATIVE,
IT WILL NECESSITATE UNDUE CONSUMPTION OF TIME, AND IT WILL
CONFUSE THE ISSUES, AND MISLEAD THE JURY
Evidence Code § 352:
The court in its discretion may exclude evidence if its
probative value is substantially outweighed by the probability
that its admission will (a) necessitate undue consumption
of time or (b) create substantial danger of undue prejudice,
of confusing the issues, or of misleading the jury.
Here, any evidence of “Retrograde Extrapolation”
is going to be predicated upon assumed hypothetical facts
that cannot be proved by the prosecution. Assumptions are
therefore of the highest speculative nature. It will create
a very high risk of confusing the issues and misleading
the jury. Moreover, it will result in a definite undue consumption
of time.
San Diego DUI Defense Lawyers point out that error in such
an assumption translates into error in the extrapolation.
Legendary Don Nichols, one of the most respected DUI defense
attorneys & author of "Drinking Driving Litigation"
knew how to properly handle possible error in assumptions.
Don pointed out to juries that his client is female, Chinese
and deceased despite obvious evidence to the contrary.
Don then explained that statistically there are more women
than men in the world, more Chinese than any other nationality,
and more dead human beings than living ones. Statistically,
then, the average person is female, Chinese and deceased.
So must be his client, according to the DUI Prosecutor.
Don further asked his juries how many of them have 2.3 children,
the average in the United States.
So why does the San Diego DUI prosecution "expert"
presume facts that are clearly untrue? Simple. It's very
expedient - it makes San Diego DUI prosecution and possible
San Diego DUI conviction after trial much easier. Which
is one more reason why you want to hire a San Diego DUI
Attorney Specialist.
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San Diego County DUI Law Center
- All Rights Reserved
