It is common for prosecutors in Oregon DUII cases to introduce evidence, through expert testimony, that purports to estimate a person’s blood alcohol concentration at a particular point in time. These estimates, called “retrograde extrapolation,” are based on “Widmark’s Formula,” an equation developed by a Swedish Physician in the early 1980′s. Widmark’s equation makes certain assumptions about the rate at which alcohol is absorbed into the blood stream and the rate at which alcohol is metabolized by the body. By accounting for a person’s weight, it is said that an expert can use this calculation to determine a person’s blood alcohol concentration hours prior to them being tested.

This calculation can be critical in a DUII or vehicular assault prosecution. Under Oregon DUII law, a prosecutor is required to provide proof that a person’s blood alcohol level was over the legal limit of .08 *at the time of driving*. Since breath or blood tests are often administered an hour or more after driving, prosecutors rely on this equation as a useful tool. Generally, the witness is a chemist from the Oregon State Police Crime Lab who is familiar with the equation and has the expertise to do the mathematical calculation. This equation can also be used to calculate the number of drinks that a person consumed.

The problem with Widmark’s Formula is that it makes assumptions about how fast alcohol is absorbed into the body and, more importantly, the rate at which alcohol dissipates from the blood stream. The truth is that the dissipation rate for alcohol varies widely among individual people. Widmark assumed that the average person metabolizes alcohol at a rate of about .015 per hour. In actual fact, that rate can vary from .009 to .040 between individuals.

Recently, the Oregon Court of Appeals ruled on the admissibility of retrograde extrapolation evidence in State v. Whitmore. Mr. Whitemore was arrested for DUII and had a BAC of .08 about an hour after the traffic stop. He claimed he had only drank 3 beers over a period of two hours. The state called a Crime Lab Expert who applied Widmark’s calculation and offered the opinion that a man of Whitemore’s size would have had to consume 7 to 10 and half drinks to be at .08 under the facts set out by Whitemore’s testimony, which painted him as a liar.

Whitemore’s lawyer argued that the state should have been required to prove that Widmark’s calculation was scientifically valid before they could have the chemist apply the calculation and offer an opinion, an argument the trial judge rejected. The Court of Appeals reversed Whitmore’s conviction, holding that the state does have to prove that the calculation is scientifically accurate before having a witness offer an opinion based on the equation. The Court noted that evidence that is scientific in nature is likely to be viewed as reliable by a jury. As such, the state should be required to prove the science, or “lay the foundation,” for the accuracy of the equation before an opinion based on that science can be presented to a jury.

This is an important ruling for Portland Criminal Defense Lawyers.

It is common for prosecutors in Oregon DUII cases to introduce evidence, through expert testimony, that purports to estimate a person’s blood alcohol concentration at a particular point in time. These estimates, called “retrograde extrapolation,” are based on “Widmark’s Formula,” an equation developed by a Swedish Physician in the early 1980′s. Widmark’s equation makes certain assumptions about the rate at which alcohol is absorbed into the blood stream and the rate at which alcohol is metabolized by the body. By accounting for a person’s weight, it is said that an expert can use this calculation to determine a person’s blood alcohol concentration hours prior to them being tested.

This calculation can be critical in a DUII or vehicular assault prosecution. Under Oregon DUII law, a prosecutor is required to provide proof that a person’s blood alcohol level was over the legal limit of .08 at the time of driving. Since breath or blood tests are often administered an hour or more after driving, prosecutors rely on this equation as a useful tool. Generally, the witness is a chemist from the Oregon State Police Crime Lab who is familiar with the equation and has the expertise to do the mathematical calculation. This equation can also be used to calculate the number of drinks that a person consumed.

The problem with Widmark’s Formula is that it makes assumptions about how fast alcohol is absorbed into the body and, more importantly, the rate at which alcohol dissipates from the blood stream. The truth is that the dissipation rate for alcohol varies widely among individual people. Widmark assumed that the average person metabolizes alcohol at a rate of about .015 per hour. In actual fact, that rate can vary from .009 to .040 between individuals.

Recently, the Oregon Court of Appeals ruled on the admissibility of retrograde extrapolation evidence in State v. Whitmore. Mr. Whitemore was arrested for DUII and had a BAC of .08 about an hour after the traffic stop. He claimed he had only drank 3 beers over a period of two hours. The state called a Crime Lab Expert who applied Widmark’s calculation and offered the opinion that a man of Whitemore’s size would have had to consume 7 to 10 and half drinks to be at .08 under the facts set out by Whitemore’s testimony, which painted him as a liar.

Whitemore’s lawyer argued that the state should have been required to prove that Widmark’s calculation was scientifically valid before they could have the chemist apply the calculation and offer an opinion, an argument the trial judge rejected. The Court of Appeals reversed Whitmore’s conviction, holding that the state does have to prove that the calculation is scientifically accurate before having a witness offer an opinion based on the equation. The Court noted that evidence that is scientific in nature is likely to be viewed as reliable by a jury. As such, the state should be required to prove the science, or “lay the foundation,” for the accuracy of the equation before an opinion based on that science can be presented to a jury.

This is an important ruling for Portland Criminal Defense Lawyers.