FST Pseudo-Science, Part I
Pseudoscience means "a discipline or approach that pretends to be or has a resemblance to science, but is based on false assumptions." Examples include astrology, psychokinesis, clairvoyance and field sobriety testing.
In a DUI trial, one of the most important parts of the evidence is known as the Field Sobriety Tests or FST's. In a previous blog, I told you that you should never perform these tests. One of the main reasons for that is just how little scientific relevance these tests have. Oh, where to begin?
The National Highway Transportation Safety Administration (NHTSA) developed the "Standardized Field Sobriety Tests" (SFST's) over a series of studies done between 1975 and 2004. NHTSA claims these studies revealed that by using three Field Sobriety Tests (the SFST's), police officers were able to discern drivers who were over the legal Blood Alcohol Content (BAC) with 78% accuracy. Through a trick of semantics, NHTSA now claims that in one study (the "San Diego Study") they were 91% accurate!
Nonsense.
Here's how you perform a proper study to validate tests: Have trained police officers do the FST's for a bunch of people, then note how often the officer is right. Then tell people the result. End of story. But that's not what NHTSA did.
Instead, NHTSA had trained police officers perform the FSTs on hundreds of drivers. But they also assessed those drivers in other ways. They interviewed them. They smelled their breath. They looked for physical evidence like open bottles. They got confessions. AND they gave a portable breath test (PBT) to every driver. THEN the officers wrote down their guess for the driver's BAC. It's patently ridiculous to claim that this was a valid test of the Field Sobriety Tests.
But wait, there's more.
FST's are not supposed to predict a particular BAC, only to indicate if they are high or low. These tests were highly accurate only if you look at how many high-BAC drivers were arrested. Nearly all of them, in fact (giving rise to that 91% figure). But they also indicated that nearly all the low-BAC drivers had a high BAC. In fact, the FSTs were only 30% accurate in identifying innocent people. That is, when the government bags nearly as many innocent drivers as it does the guilty, it declares success.
Would you fly on an airline that landed safely 91% of the time? What about 30% of the time?
One more thing. That 30% relied solely on one officer. Six of the seven officers were wrong with 100% of the innocent drivers (that is, even after the interview, the FST's and the PBT, they identified every innocent driver as being over the limit).
Only one of the seven officers was ever correct about the innocent drivers, and he was correct about those innocent drivers 100% of the time. When the FST's were wrong, his estimates were right anyway. How did he do it? Well, I wasn't there. But I'll just say that his estimates exactly matched those measured by the PBT every time.
Once again, YOU DO NOT HAVE TO PERFORM FIELD SOBRIETY TESTS. Don't. Just politely tell the officer you won't do them.
PS: I am NOT saying the police officers did anything wrong. They did what they were supposed to do. I am saying that the data was reported in a deliberately misleading fashion and are used every day to prosecute innocent people.