Backdoor Breath Testing 2: Scientific Community's Opinion on Measurement Uncertainty

Posted On May 17, 2016 by Charles Ramsay

You've been arrested on suspicion of DWI; you were placed in the back of a cop car, brought to a police station, and told to blow into strange looking device that looks like a computer straight out of an 80's science fiction movie with an E-cigarette attached to it. This machine spits out a number, let's say .09. This number (.09) will now be used to charge you with a crime, revoke your driver's license, force you to get "whisky plates,| and potentially even take your vehicle. It is a powerful number indeed.

But just how accurate is that number as an indication of your true alcohol concentration? Quite simply, we don't know, and neither does the Minnesota BCA or law enforcement. That's because all measurements need to be reported alongside another number that tells you just how accurate (or inaccurate) the measurement actually is â?? the concept of |measurement uncertainty.|

That is not our opinion; that's the opinion of every single scientific body in the world. It's a well-established practice everywhere. For example, the National Academy of Sciences (NAS)â??a society of distinguished scholars, established by Congress, and charged with providing independent, objective advice to the nation on matters related to science and technologyâ??says all breath tests |need to be reported, along with a confidence interval that has a high probability of containing the true blood-alcohol level.|

The National Institute of Standards and Technology (NIST) agrees, saying that test results are only estimates of the true value of what is being measured, and are |complete only when accompanied by a quantitative statement of its uncertainty.| Similar opinions are also held by distinguished authorities in the scientific community, such as Rod Gullberg and A.W. Jones. Specifically, Gullberg states that all measurements |that matter| must be reported with their full range of measurement uncertainty

The International Standards Organization (ISO), the |gold standard| when it comes to reporting measurements, is adamant on the importance of measurement uncertainty, stating that it is |essential to the interpretation of the result,| and without it, it is |impossible| to know if |laws, based on limits, have been broken.| The ISO also warns that failure to accompany test results with a measurement uncertainty may result in |incorrect prosecution in law.|

With such a universal consensus in the scientific community, there is no doubt that breath test results must be accompanied by a measurement uncertainty. This is the only way for judges and juries to evaluate the accuracy of the test result before issuing harsh sanctions and criminal penalties.

This isn't anything groundbreaking; as we told you in the first post of this series, the Minnesota BCA already reports the full measurement uncertainty every time they measure the alcohol in a blood or urine sample. What's baffling (especially in light of all the scientific consensus we showed you above) is that the Minnesota BCA has elected to almost completely ignore measurement uncertainty for breath tests. Later in this blog series we will discuss the BCA's mind-numbing arguments as to why they feel their breath tests in Minnesota do not need to comply with this fundamental requirement. For now, just know that breath tests in Minnesota are fundamentally flawedâ??and that's not our opinion, that's the opinion of organizations like the NAS, ISO, and NIST, as well as highly regarded researchers like Rod Gullberg and A.W. Jones.

Next Post:

Part 3: Scientific Community Regarding Traceability and Accuracy