Nationally recognized DUI guru Lawrence Taylor has one of the best blogs on the net focused on DUIs. I make The DUI Blog a standard stop on my daily tour through the blogosphere. One of the recurring themes you’ll find there is the inherent unreliability of the Breathalyzer machine regularly used by police to “confirm” the Blood Alcohol Content (BAC) of DUI arrestees by sampling their breath. Taylor is right: the Breathalyzer is junk science squared, flawed not only in theory as a general instrument for making the purported translation from breath to blood, but even more so in practice by virtue of its routine misuse.

Taylor eloquently describes both the inherent unreliability and the routine misapplication. But in light of such critiques (and they are legion), one has to ask: “How is it that the law forbids any mention in court of a Polygraph (”lie detector”) result on the theory that its operation is based on suspect science, while the results of the roundly criticized Breathalyzer are routinely admitted into evidence to convict and jail motorists?” What’s up with that?

Good question, indeed. Both machines share the intrinsic flaw of over-generalization of isolated scientific principles stretched to scientifically unsupportable conclusions; both are misused by lazy or indifferent operators who routinely fail to adhere to the disciplines mandated by manufacturers in order to assure reliability (notice the implicit assumption of unreliability when said discipline is not employed); and both can be fooled by a savvy subject. Both machines focus on certain physiological changes in body chemistry and then attempt to give meaning to these changes.

There are lots of reasons why courts have consistently denied admissibility of one machine while regularly endorsing the other. One is a general reluctance to attempt to assess internal states of mind. Our life experience and intuition tell us that the inner thoughts of a human mind cannot be knowable with any certainty. Indeed, I believe such attempts are perceived as an invasion of the ultimate expectation of privacy, a violation of our innermost sanctum, and therefore marginalized in value as a function of our rejection of the invasion. And yet science is replete with examples of body chemistry changes associated with particular forms of mental activity, to the point where specific locations within the brain can be accurately pinpointed for predictable chemical change response in connection with specific mental activity. It’s not really that far-fetched an idea to propose that certain types of mental stimuli will have predictable and measurable physical consequences.

The breath machines, on the other hand, don’t attempt to document any internal mental state. They simply measure one chemical state (the amount of ethanol in a sample of breath) and attempt to translate this value into another chemical state: the amount of ethanol by weight in the subject’s blood. Somehow we view this correspondence as more reliable because it doesn’t ask us to make the leap of faith in trying to ascertain what’s happening inside our mind. Instead, it’s just doing math. Measure my blood, no problem, but don’t be messing with my head.

Another reason for breathalyzer chauvinism is the MADD rush to deal with the DUI “problem”. No politician will ever lose a race for failing to endorse the polygraph, but they will fall over themselves trying to introduce legislation making it easier and easier to admit breath machine evidence into court to convict the drunk driver, one of the most popular whipping boys around the courthouse. You can imagine how eager most politicians would be to endorse any science that could reliably tell when someone is lying.

In the end, each of these machines produces information that may have some supplemental utility in helping us to understand a complete picture. But neither is adequate alone to make the kinds of determinations that can wind up sending someone to prison. I know a lot of polygraph examiners and Breathalyzer operators, and the best of them will agree with me that these machines are tools that can provide useful information in the hands of a capable and disciplined operator, but cannot be trusted alone to become judge and jury.

RP

This entry was posted on Monday, November 14th, 2005 at 9:58 pm and is filed under Hardware, Junk Science, DUI. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.