Comments on: Breathalyzers: 40% Margin of Error is Acceptable Accuracy?

By: Lawrence Taylor

Lawrence Taylor — Fri, 23 Jun 2006 15:31:42 +0000

ToxLab Guy:
I’m not sure what you mean by an “atypical circumstance”. I agree that a high majority of tests will reflect duplicate test results within the + / – .02% range. Of course, my point is not that law enforcement is not getting results within this range, but rather that this range is entirely too broad: a permissible second-test variation of 40% is no indication of acceptable scientific accuracy — nor of legal proof beyond a reasonable doubt.
As to my “improperly referring” to a 40% range of error, I use this illustrative figure because the second test is designed as an accuracy check on the first. The question is what the permissible range is for that second test for there to be legal “accuracy”. If the first test is .10%, the permissible range is .08%-.12%, which represents a .04% range. This means that the accuracy check on a .10% reading is 20% in either direction, or a total allowable range of 40%
Of course, the 40% depends upon the numerical value of the first test; the numerical range varies with the vlaue of the initial test. I could, for example, have chosen .08% as an example, in which case the range of error would be 50%. I chose .10% as an example because (1) mathematically it is easier to illustrate the point, and (2) in my involvement with thousands of DUI cases over 30 years, it has been my experience that the majority of DUI test results fall within the .08% to .12% range.
It may well be that we are engaged in semantics. In any event, I appreciate your well-reasoned comments and continuing contributions to this blog.

By: Thomas W. Shaffer, Esq.

Thomas W. Shaffer, Esq. — Thu, 22 Jun 2006 21:40:20 +0000

Dear Mr. Taylor:

I practice in Pennsylvania and the district attorneys rely on Commonwealth v. Rick, 366 A.2d 302 (1976) to circumvent the hearsay rule. In the above-referenced DUI case, a lab report was admitted over a hearsay objection because the police testified that he had spoken to the chemist who related he would be on vacation during the preliminary hearing but would be available to testify at trial.

While I’m aware that this has been standing law for a very long time, the problem I see again and again is that the police do not contact the crime lab to verify that they will be available to testify at trial, but testify that the chemist will be available to testify when in fact they have not contacted anyone from the crime lab.

While I have argued to many magistrate’s without success that Rick does not support the facts described above, is there a case to support my position. i.e. do police need to obtain veritication each time or can they just rely on the assumption that someone will appear to testify as a chemist?

If you would be so kind, I have another question. If someone is validly parked in a restaurant parking lot and a police officer allegedly made arrests there within the past 2 years, is there a Pennsylvania or U.S. Supreme Court case that shows that when a fully uniformed police officer, driving a marked police car, shines his spotlight onto defendant’s said car (without blocking the defendant’s car from leaving), that the police officer made a show of force that necessaitates proof of reasonable suspicion for the stop to be valid?

I am aware that the other arrests must be close in time to make this parking area suspect, but I cannot find a case that only has the facts stated above. There are many other cases related but they all seem to have additional facts that change the situation my client faces.

Thanking you in advance for your help. I love to read your website.

tommyshaffer@hotmail.com

By: Tox Lab Guy

Tox Lab Guy — Wed, 21 Jun 2006 18:03:05 +0000

However, that is an atypical circumstance, and those error ranges are designed to flag the wayward instrument. If you were to look at a large population of replicate results, a very high majority of those would be well within the 0.02 g/dL range. I would be interested in seeing that data, but I doubt it would serve your purpose much.
In addition, your example improperly refers to a 40% range of error in the second test. A more accurate depiction would be ± 0.02 g/dL error, and the difference is important. In your example, the replicate readings can be 0.10 g/dL and any one of the following: 0.08 g/dL (20% less), 0.09 g/dL (10% less), 0.10 g/dL (no difference), 0.11 g/dL (10% more), and 0.12 g/dL (20% more). Those numbers are dependent upon the fact that you chose 0.10 g/dL as your benchmark. A higher (or lower) BAC will change those percentages, because the ± 0.02 g/dL requirement is fixed, regardless of the BAC.