This is a big question to answer in what will be a fairly short article, but I’m going to do my best. But before I get too far, let me point out that I am a DUI lawyer. This means, invariably, my answer to the question posed in the title will be no, DUI breath tests aren’t really scientific.
Unlike most people, however, I’m going to actually give you a reason why. And this reason is a big reason – it destroys the entire idea that a DUI breath test is scientific at all.
If you’ve ever taken a statistics class, then you have a pretty good idea of what a level of uncertainty is. It, essentially, is the percentage with which you can be certain that a specific measurement falls within. As you zero in on a specific number, the level of uncertainty gets smaller and smaller. Let me give you can example.
Let’s say you want a cup of milk. So, you take out your measuring cup and fill it up. Now, you probably understand that it is extremely unlikely that there is exactly one cup of milk in the measuring cup. A measurement that precise is impossible to predict. But, you can probably be about 99% sure that that measuring cup has anywhere from .9 cups of milk to 1.1 cups of milk. That is uncertainty.
But, in DUI breath (and blood tests) typically no level of uncertainty is calculated. That means when the toxicologist takes the stand they are saying they are 100% positive that the measurement provided from the test is accurate. There is only one problem with that – that is an impossible statement to make. No where in science are absolutes provide. And to do so is bad science.
Scientific proof is centered on the ability to measure, to recreate conditions, and to prove theories. Without a level of uncertainty, there is no way to determine just how accurate this test is. And without knowing the range of inaccuracy, it is impossible to know if your breath test is actually above or below the legal limit.
If you are charged with a DUI and your breath test is anywhere near the threshold (.08), it is important to hire a DUI attorney that understands the implications of levels of uncertainty and can explain them to a jury. In my hometown, for example, only a really good Seattle DUI attorney takes the time to understand the science behind the breath test and uses it to exploit the weaknesses in the prosecutor’s case.
To answer the question, no, DUI breath tests aren’t scientific. They don’t meet the minimum standards of accepted science. Think about that the next time you hear about someone being charged with DUI.
