This web site gives the opinions of Dr. Greg Kane. Everything you read here is expressed only as my personal opinion.

AROUND the country, DUI defense attorneys form organizations, give seminars and share trial strategies to overcome FST evidence. Prosecutors do the same, from the other direction. The two sides bicker about mechanics. Did the officer follow procedure exactly? Did the officer consider medical conditions that cause incoordination?

What no one does is doubt the NHTSA validation contractors' analysis of what a meticulously administered coordination test actually implies about alcohol impairment. The driver failed the FST. No one asks, "Exactly what does that mean?"    Field Sobriety Test .info shows you how science answers that question. These web pages introduce you to the basics. The articles linked at the bottom of this page explain details.

Claimed Accuracy	The government's fundamental claim is that if you know a person's Field Sobriety Test score you know their Blood Alcohol Concentration. The National Highway Transportation Safety Administration has paid for several studies claiming to discover that officers "using" FSTs are "extremely accurate"—about 90% accurate—at identifying driver's with high BACs. The "extremely accurate" result is a statistical trick. Using that trick you can set up your "validation" study beforehand, so it is certain to “discover” whatever arrest accuracy you’ve been paid to validate.
Raw Data	Available to you here for the first time is the raw data from one of the NHTSA's FST "validation" studies. Now you don't have to take the NHTSA's word for it that FSTs are "extremely accurate." You can review the raw data and see for yourself.
Scientific Accuracy	What the raw data proves is that, to a first approximation, the FST works this way: 1. Everybody fails, 2. Officers ignore the test, and arrest or release drivers based on other criteria.
Secret Evidence	FST accuracy data is secret. The government makes extravagant claims about the accuracy of the FST, but it has never published and now refuses to release the raw data on which those claims are supposedly based.

In depth
The web pages here at Field Sobriety Test .info give you only the outline and the barest results of how science answers the question "Exactly what does a failed FST mean?" The articles linked below explore the basic science in more detail.

The following papers first appeared in Trial Talk, the journal of the Colorado Trial Lawyer's Association.

Percentages of Percentages, Why "Validation" Studies Fail to Validate
OPEN

Take home
The "accuracy" of a test is a technical mathematical statistic that does NOT reflect the likelihood that a person who fails the test is impaired.

From the article:

The NHTSA's mathematical "accuracy" formula is a triple percentage. It depends not just on the fundamental properties of the roadside sobriety test, but also on the percentage of impaired drivers in the study group. The result is the formula gives different answers, depending on the balance of impaired and innocent drivers picked for the study. Simply by adjusting the balance of impaired and sober drivers in the study group, the NHTSA can dial in the accuracy its research "discovers."

For example, in the Colorado Validation Study NHTSA contractors chose study drivers in a way that led to the discovery of an officer arrest accuracy of 93%. But, keeping the fundamental accuracies exactly the same and simply reversing the percentage of impaired and innocent drivers chosen to be studied would have changed the officer arrest accuracy to 52% - a coin toss.

Trial Talk, August/September 2006, pg 33 ff
347 K pdf opens in a new window.

Posted with permission of Trial Talk®. © Colorado Trial Lawyers' Association.

Field Sobriety Tests: How Basic Science Proves They Have Little Power to Tell Impaired From Sober
OPEN

Take home
The number that predicts the probability of impairment is the Positive Predictive Value. The PPV of the FST is terrible.

From the article:

Look at the results for the Colorado Validation Study. Drivers with a 1% chance of impairment, when they failed the Colorado Validation Study roadside sobriety test, still had only a 4% chance of being impaired. A driver with a 5% likelihood of impairment, after an “arrest” answer, had only a 16% chance of being impaired. All across the table, the FST added only a few percentage points to the probability of guilt - never enough to turn unlikely into likely.

That’s the point. It’s not that you have to do a fancy positive predictive value mathematical accuracy statistic calculation for every DUI defendant. The point is that roadside sobriety tests have been studied and restudied and studied again. And over and over and over standard scientific analysis of the results prove exactly the same thing. Roadside sobriety tests have no meaningful power to turn unlikely into likely - no meaningful power to identify impairment. FSTs do not work.

Trial Talk, October/November 2006, pg 57 ff
255 K pdf opens in a new window

Posted with permission of Trial Talk®. © Colorado Trial Lawyers' Association.

From the article:

Two tricks fix validation studies so any FST can come off "extremely accurate."
Trick One: Move the FST's inaccuracy over onto the innocent drivers.
Trick Two:  Hide the innocent drivers.

....Please realize, all Trick Two does is hide the Innocent Driver Inaccuracy. It hides the inaccuracy by hiding innocent drivers from the "overall accuracy" calculation. Trick Two does not fix the Innocent Driver Inaccuracy. According to the NHTSA, officers using standardized FSTs still arrest 29% of the innocent drivers they assess.

....The results of reversing Trick Two are in line 9 [of table 1]. As soon as you reverse Trick Two, in study after study, the "overall accuracy" of the roadside test plummets to a number close to the accuracy of a coin toss. The two statistical tricks are the direct cause of the high accuracies "discovered" in NHTSA validation studies. But for the two tricks, FST validation studies fail to validate.

Posted with permission of Trial Talk®. © Colorado Trial Lawyers' Association.