Just How Accurate Are Field Sobriety Tests?

In order for someone to be convicted of driving under the influence, law enforcement must collect evidence showing that they were intoxicated while driving. However, in order to collect evidence, they must conduct a search, and searches are usually only authorized once they place someone under arrest. Because law enforcement can’t simply arrest someone for driving under the influence based on a “gut feeling” or they risk a wrongful arrest and unreasonable search, they must first establish “probable cause.” To do this, they use what are known as field sobriety tests.

Field sobriety tests are a standardized group of tests that law enforcement use to analyze someone’s intoxication level. If someone shows enough signs of intoxication, then enforcement make the arrest, which authorizes them to conduct a chemical test on the suspected individual. With how important these tests are, it’s reasonable to expect that the tests are accurate and show few to no errors.

But is that the case? Our blog takes a closer look at the three commonly-accepted types of field sobriety tests and discusses their shocking accuracy statistics in greater detail.

The Walk-And-Turn

The walk-and-turn test involves the accused being required to walk heel-to-toe in a straight line along the ground (sort of like they’re on a balance beam) for a certain number of steps before turning on the spot without lifting their feet and then walking the same number of steps back. The task essentially requires someone to focus on both a physical task (walking in this unique fashion without losing balance) and a mental one (counting the number of steps and following instructions). Doing both of these things simultaneously is generally far more difficult for intoxicated individuals.

However, even with standardized procedures and accurate administration of the tests, studies showed that the test only gave an accurate result 68 percent of the time—slightly less than seven out of ten.

The One-Leg Stand

The one-leg stand test involves the suspected individual being required to stand on one leg with their other leg pointed outward and toes pointed up while also being required to complete a mental task, usually counting to 30 by using the “one-one thousand, two-one thousand” method. Like the walk-and-turn, it might seem simple enough, but the truth is it’s a difficult task for just about anyone. Standing on one leg for an extended period of time is difficult for even completely sober people, let alone those who are tired or struggle with balance to begin with.

The one-leg stand test, even after standardization, yielded an accuracy rate of just 65 percent, which means that between three and four out of every ten tests yielded an inaccurate result!

The Horizontal Gaze Nystagmus

The horizontal gaze nystagmus test is perhaps the most relied-upon test because of how easy it is to conduct it and how difficult it can be to fool. Essentially, the test simply analyzes someone’s ability to control their eye movements, which becomes more difficult as your become more intoxicated. The officer holds a pen, pencil, their finger, or a small flashlight up to the test subject at approximately eye level then asks the subject to follow it with their eyes without turning their head as they move it slowly back and forth. The movement should cause an intoxicated subject’s eyes to begin to twist or shake because of the lack of control over the muscles that coordinate eye movement.

This test is by far the most accurate of the three, but still only yields an accuracy rating of approximately 77 percent.

Using multiple tests on a subject yielded much better results, as multiple tests provided even better evidence for greater accuracy. However, even when all three tests were used together, a study conducted by the NHTSA and Southern California Research Institute (SCRI) found that they were accurate only 82 percent of the time. That means slightly less than one out of every five tests yielded an inaccurate result!

For this reason it’s critical that you talk to a Birmingham DUI attorney about your case if you’ve been charged with driving under the influence. Your case may have been wrongfully influenced by a faulty or erroneous field sobriety test, leading to an unlawful arrest and illegal evidence collected against you.

Call Tidwell Law Group at (205) 536-7770 to request a consultation and start discussing your case in detail today!