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Retrograde Extrapolation – San Diego DUI guess of higher BAC at time of driving

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.

This website & linked blog is made available by this law firm for general information purposes only and to provide a general understanding of the law, not to provide legal advice. Readers of this website/blog are cautioned that reading the website/blog does not create a lawyer-client relationship between the reader and this law firm.

By: Rick Mueller

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