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The Interplay Between Reasonable Doubt and Measurement Uncertainty in Michigan DUI Cases

Sep 2nd, 2016 DUI Defense

If you are charged with DUI in Michigan then the police probably claim that you were over the legal limit. To support their opinion the police will base their case on the results of either a breath or blood test.

When it comes to Michigan DUI cases, and in particular the application of science to the Michigan DUI laws, nothing is ever quite a simple as it seems.  This is especially true when it comes to breath and blood testing.  Just because a piece of paper says that you were over the legal limit, this does not mean that the police have proven, beyond a reasonable doubt, that you are guilty of drunk driving in Michigan.

At the most basic level, a breath or blood test result is a measurement; in this case one that hopes to determine, with a high degree of certainty, whether your blood alcohol level was above or below .08.  If the science of measurement is applied to this breath or blood test result, what does that tell us about whether or not you were actually drunk driving in Michigan?

A recent book authored by Ted Vosk and Ashley Emery looks at this particular question.  The title of the book is Forensic Metrology: Scientific Measurement and Inference for Lawyers, Judges, and Criminalists(International Forensic Science and Investigation); and what follows is a partial quote from the Amazon book page:

Forensic metrology is the application of scientific measurement to the investigation and prosecution of crime. Forensic measurements are relied upon to determine breath and blood alcohol and drug concentrations, weigh seized drugs, perform accident reconstruction, and for many other applications. Forensic metrology provides a basic framework for the performance and critical evaluation of all forensic measurements. It enables forensic scientists to better develop, perform and communicate forensic measurements; lawyers to better understand, present and cross-examine the results of forensic measurements; and judges to better subject testimony and evidence based on forensic measurements to the appropriate gatekeeping analysis.

As a general and very basic premise, all measurements have some degree of uncertainty associated with them.  Consequently, without a known range of uncertainty a measurement is meaningless.  This is why it’s possible to say that unless the breath or blood test result in your case is accompanied by a statement about the associated range of error, it really doesn’t prove that you violated Michigan’s drunk driving laws.

Michigan’s toxicology lab has only recently started reporting an uncertainty level in their blood alcohol reports.  Since they first started reporting this uncertainty level there has been debate as to whether or not the uncertainty reported was properly calculated.

The same is true of breath test results in Michigan drunk driving cases except that breath tests are not currently accompanied by an uncertainty range.  This is because the range of uncertainty has not yet been properly calculated. What this all means is that every day innocent people are undoubtedly arrested, charged and convicted of drunk driving in Michigan.

If you have been charged with drunk driving in Michigan, insist that the prosecutor prove the charges against you beyond a reasonable doubt.  This means the police must at least properly calculate and report the amount of uncertainty in the breath test you were given.  You may just find out that they are unable to do so, and without this information, they may also be unable to prove your case beyond a reasonable doubt.