Just How Accurate Is Minnesota's DWI Breath Test Machine?

Posted On July 15, 2016 by Jay Adkins

(Author's Note: The following long post is geared primarily towards defense attorneys trying to keep up with the latest developments involving Minnesota's breath testing setup. If you're not a defense attorney, you may want to skip this post; we'll be providing further information later in the week that is geared towards lay persons. Of course, nothing is stopping you from continuing on â?? this is fascinating information!)

For the last several years, the Minnesota Bureau of Criminal Apprehension has been reporting the uncertainty data that applies to all blood- and urine-alcohol tests done in their laboratory. Rather than reporting a raw number ("this sample was 0.09|) the lab would, on the face of the report, include the uncertainty interval with every measurement (|this sample was 0.09 ± 0.004 with a 99.7% confidence interval|). That information provided after the little |±| was absolutely crucial â?? it tells us how inaccurate the measurement is, how likely it is that the measurement was at or above the legal limit, and effectively how much |trust| we could put into the analysis. By the way, don't think that the BCA released this data because they wanted to be transparent; they openly admitted that they only did it because it was the bare minimum necessary to keep themselves from losing their accreditation.

For the last several decades, the Minnesota Bureau of Criminal Apprehension has not been reporting the uncertainty data that applies to breath tests. There, all they were willing to report was the raw number (|this sample was 0.09|) and drivers, jurors, and judges were each supposed to just |trust them| and conclude that the number reported was the only number that mattered. Funny enough, because their accreditation did not formally require them to release this particular number, the BCA felt comfortable completely ignoring the scientific need to report their breath uncertainty . . . "close enough for government work" indeed, eh?

Now everyone knows that lab-run blood and urine tests are way more accurate than field-run breath tests. How much more inaccurate? That's always been the $10,000 question. Put plainly, how many people were being convicted based off of shoddy science?

Now we know: we now know that, roughly speaking, you cannot say that a Minnesota driver was above the legal limit of 0.08 if their breath test reported an alcohol concentration any lower than 0.091. If someone tested less than 0.181, you cannot say that they were actually twice the legal limit. That's because the BCA, after facing incredible pressure from our firm (and all of the attorneys who took the tools we provided them and added to that pressure), has finally released their interpretation of how much uncertainty actually affects a Minnesota breath test.

We're going to provide you with that data at the end of this post; in any given case, you will be able to obtain it directly from the prosecutor/attorney general's office with a discovery demand, but this data is so crucial to the interpretation of any breath test result that it should really be included with every test report. But before we get to that point, please read on.

This data is crucial for a variety of reasons, the first being that we're finally getting to use real science in the courtroom. But more importantly, every year we've seen thousands of drivers charged with (and likely convicted) of DWI based on scientifically flawed test results (the relevant data starts on page 5 if you are curious enough to actually click that link). So in answer to the question of "how many wrongful convictions?" we can safely say it reached to thousands of drivers annually -- drivers who were told they were over 0.08, or over 0.16, when the fundamental truth is that they were not. That's chilling.

And that's honestly not just a failure by the BCA, or by our courts â?? that's a failure of the defense bar. It's a failure we're about to correct, but don't think that correcting it is going to be as easy as bringing the data we're about to provide you into court, waiving it around, and yelling |not guilty! NOT GUILTY!| It took us a year of intense litigation to finally get these numbers released, and don't think for a second that this means the fight is over. No, now the fight has just shifted gears.

So get educated. If you don't know what the term |traceability| is, you're committing malpractice as a defense attorney. If you don't know how instrumentation bias effects the adjusted mean before applying the appropriate confidence interval, the data we've provided below won't do you or your client any good at all and you should refer them to a competent attorney who can actually help them.

So bone up on the science. In fact, here's a primer: the complete table of contents to our blog series detailing how to expose the flaws in Minnesota's breath testing program. Read it, get familiar with it.

Part I: Why Use Breath Tests At All?

Part II: Scientific Community's Stance On Measurements

Part III: Measurement Traceability & Accuracy

Part IV (a): Breath Tests In Implied Consent (License Revocation) Cases

Part IV (b): Breath Tests in Criminal Cases

Part IV (c): Attempts To Keep Science Out Of The Courtroom

Part V: Court Transcripts

Part VI: Science Prevails! BCA Admits Defeat, Admits To Major Inaccuracies

Still with us? Okay, here's what you slogged through all that text for: the complete uncertainty data, as provided by the Minnesota BCA.

Use it wisely. With great power comes great responsibility.

Coming up, we'll provide a simplified version of these challenges to help explain this astonishing turn of events to people who may be facing DWI charges right now. We'll also start explaining some of the pitfalls that can trap unsuspecting defense attorneys trying to use this information to help their clients win their cases. Stay tuned.