Retrograde Extrapolation Might Be an Effective Defense to OWI Charges

If an expert witness is aware of the amount and timing of alcohol consumption, as well as some additional information, he or she can testify about a person’s level of intoxication over time. 

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Can an expert determine a person’s level of intoxication at the time of driving, as opposed to the time of testing?

Retrograde extrapolation can be used to determine what someone’s bodily alcohol content was at the time of driving by utilizing a mathematical equation. By using the BAC levels determined through blood or breath testing during the OWI investigation, time, and other factors, a reasonable estimate can be made. Just as a prosecutor may use these calculations to prove that someone was intoxicated or impaired, a skilled and experienced OWI defense attorney can use the same calculations to create reasonable doubt.

What Does Retrograde Extrapolation Mean to Me and My Drunk Driving Case?

Retrograde extrapolation” may sound like a fancy legal term that is hard to understand unless you are a lawyer or doctor, but despite its unusual name, it is actually a very simple idea. Retrograde Extrapolation, or RE, is a mathematical calculation. It is the rate at which a body eliminates alcohol multiplied by how much time has passed. In theory, this calculation can tell you what a person’s blood-alcohol level (BAL) was at some time in the past.

As you can imagine, that is easier said than done. All people eliminate alcohol at different rates. Other factors also influence the elimination rate such as what and how much you had to eat, the type of alcoholic beverage you drank, your body size, and the state of your overall health, just to name a few examples. Elimination rates even differ between men and women and people of different ages. The reason RE is permitted as a defense to OWI (Operating While Intoxicated) charges, despite these variables, is because medical research shows that there is enough of a percentage of the population that processes alcohol similarly to make RE acceptable for evidentiary purposes in court. In other words, it has been decided that RE is a “good enough” and “reliable enough” way to argue a BAL was at a certain level at the time of driving.

Blood Testing in OWI Cases

Retrograde Extrapolation Can be Used as a Shield or a Sword

Although the prosecution frequently uses a retrograde extrapolation argument to prove that a defendant’s blood-alcohol level was above the legal limit, the defense lawyer can also use the science as a defense. In many cases, the BAC of the defendant is rising and Retrograde Extrapolation can be used to raise a reasonable doubt about the level of the BAC at the time of driving.

How Can a Great Criminal Defense Attorney Deal with Retrograde Extrapolation Evidence at Trial?

Due to the various rates of elimination and the different factors which impact it, an expert is needed to explain RE to the jury for the prosecution. A defense attorney will also want their own expert to challenge the analysis of the prosecutor’s expert, and provide their own estimation of what the BAL was at the time of the driving. At the very least, the defense attorney will need to hire an expert to explain the prosecutor’s expert’s RE estimation of BAL so that the defense attorney will be able to effectively cross-examine the prosecutor’s expert.

If the defendant has a court-appointed attorney, typically such an attorney will need to ask the court for special expense costs to hire such an expert. Often times the court will be reluctant to spend public funds on an expert witness in OWI cases. The prosecution has virtually no limit to what they can pay to get the best experts available. Many times, these cases end up being a “battle of the experts” and the lawyer’s ability to make the most of the expert’s testimony can be the single deciding factor in the success or failure of the defense.

The government will almost always have a prosecutor with vast experience handling OWI cases. There are no court-appointed lawyers who exclusively handle OWI or DUI defense. That is why it is so important to have a reputable, highly experienced retained criminal defense attorney on your side in a drinking and driving case. He or she will know who the best experts are in the field, and will know how to utilize them to get you every possible advantage. In fact, once a lawyer gets a reputation for successfully defending these cases, prosecutors will start to offer deals to make cases “go away” rather than litigate a tough issue before a jury.

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Top-Rated Criminal Defense Attorneys to Rebut Retrograde Extrapolation Arguments

The dedicated, experienced and zealous defense attorneys at LEWIS & DICKSTEIN, P.L.L.C. have successfully represented thousands of clients on felony and misdemeanor charges in Oakland, Macomb, Washtenaw, and Livingston counties and throughout all Southeast Michigan. We have a well-earned reputation for providing the highest quality defense and aggressive representation, while showing empathy and care for each client.

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