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Is the Partition Ratio Used to Measure Intoxication a Flawed Scientific Principle?

One of those scientific principles that is utilized to determine how much alcohol supposedly is in somebody’s system is based on something called a “partition ratio.” There’s an average partition ratio that’s used to determine how many molecules of alcohol in somebody’s blood equate to the molecules of alcohol in that person’s breath. This average is used to report breath test results (BrAC – breath alcohol concentration). However, each person has different physiological make up. Therefore, someone may have a partition ratio different than the average.

Can Your Physiological Make Up Affect Your Partition Ratio?

The ratio that’s been used to determine the breath test results is 2,100 to 1. Yet, a person may have a higher partition ratio or a lower partition ratio and that can mean the true breath test result is not accurately reported. Two people may be the same exact height and weight, and they can drink the same amount of alcohol, but if they have different partition ratios, they’re going to have different breath test results.

Different Partition Ratios Produce Different Breath Test Results

Interviewer: How different could it be?

Kevin: It all depends on the partition ratio. For example, the man who has an average partition ratio of 2,100 to 1 blows into the machine after having five beers and the test result is a .12%. Another man, who is physically similar to him and had the same amount of alcohol in his system at the time of breath testing, but a lower partition ratio (e.g., 1,700 to 1), will end up producing a lower breath test result. As well, a person with a 3100 to 1 partition ratio would end up with a much higher breath testing result than the other two men.

Interviewer: How much difference in partition ratios are there amongst people that you’ve seen?

Partition Ratios Are Variable

Kevin: The problem is that partition ratios change. Unless, I send somebody right out to have his or her blood tested and partition ratio determined, it really can’t be determined.

Current Court Rulings Have Established Partition Ratios as a Measure of Intoxication

More important, the courts don’t care. If I found that my client has a higher partition ratio than 2,100 to 1, the courts do not consider this admissible evidence, because they’ve determined that 2,100 to 1 is the average for all the people who go through breath testing.

They have determined that somehow that’s a fair measure of the alcohol in their systems when in fact some people may be higher on that range or lower on that range.

Results Derived Through Testing that an Individual Has a Different Partition Ratio than the Courts Are Currently Using Will be Inadmissible

Interviewer: Even if you have clients that have their blood tested and their partition ratio is 1,600 and that would skew the reading by 35%, you can’t even present that to the court?

Kevin: The court would not let you present that evidence. The New Jersey Supreme Court has stated that 2,100 to 1 is the average partition ratio and that’s how the machine has been programmed to determine final breath test results. As long as the machine is in proper working order and has been operated properly that’s all they care about.

New Jersey DWI Info Guide

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