How effective are these field sobriety tests?
Consider the research funded by the National Highway Traffic Safety Administration (NHTSA), which resulted in the later adoption of the so-called “standardized” field sobriety tests.
In a study, researchers determined that the three most effective field sobriety tests (FSTs) were walk-and-turn, one-leg stand, and horizontal gaze nystagmus. Yet, even using just these supposedly more accurate tests, the researchers found that 47 percent of the subjects who would have been arrested based upon test performance actually had blood-alcohol concentrations of less than the legal limit of. 10 percent. In other words, almost half of all persons ‘failing” the tests were not legally under the influence of alcohol!
Later, these same researchers conducted further tests in an attempt to improve the credibility of the proposed “standardized” battery of FSTs. The error rate improved somewhat: The false results dropped to 32 percent-i.e., “only” a third of all persons judged to be guilty by these tests were, in fact, innocent.
These tests are unfamiliar to most people and not well practiced making it more difficult for people to perform them. As few as two miscues in performance can result in an individual being classified as impaired because of alcohol consumption when the problem may actually be the result of the unfamiliarity with the test.
It appears the NHTSA-funded researchers used methods that ensured improved reliability figures. Apparently, to reduce the number of borderline subjects (those with blood-alcohol levels of, say, .09 or .11 percent), most of the subjects received either excessive amounts of alcohol so that their BACs were elevated to .15 percent, or very small amounts so that they were below .05 percent.
NHTSA conducted a study to determine the efficacy of the various field sobriety tests. The study found that “at present, the tests and procedures used vary between local agencies and officers” and that “for many of these tests, the relationship between performance and specific BAC levels has not been well documented.” As a result of this and other studies, NHTSA now recommends only three field sobriety tests: walk-and-turn (walk-the-line), one-leg-stand, and nystagmus.
Another group of researchers tested the efficacy of the proposed standardized FSTs. The study involved testing the ability to determine whether a suspect’s blood-alcohol level was above or below. 10 percent — that is, whether he was “under the influence” in most states. The test, conducted under laboratory conditions, indicated that the walk-and-turn tests resulted in a correct assessment 75.1 percent of the time, the one-leg-stand 75.5 percent, and nystagmus 81.8 percent; when all three were given, a correct determination was arrived at in 83.4 percent of the cases. Put another way, these “improved” FSTs still identify roughly one-fourth of innocent DUI suspects as guilty — and this presumes honest and accurate administration of the tests by an experienced officer under ideal laboratory conditions.
Later, many of the original researchers at the Southern California Research Institute who had been federally funded to come up with a standardized battery published findings of their research. The study concluded that FSTs do not accurately measure driving impairment. Researchers recognized that such tests are designed to determine balance, steadiness, and reaction time but concluded that a connection between these factors and driving ability “is not apparent since neither a steady stance nor simple movement time is essential to the safe operation of a motor vehicle.” While conceding that field sobriety tests may indicate the presence of alcohol, the researchers found that they do not necessarily measure driving ability.
Dr. Spurgeon Cole of Clemson University conducted a study on the accuracy of FSTs. His staff videotaped 21 individuals performing six common field sobriety tests, then showed the tapes to 14 police officers and asked them to decide whether the suspects had “had too much to drink to drive.” Unknown to the officers, the blood-alcohol concentration of each of the 21 subjects was .00 percent. The results: 46 percent of the time the officers gave their opinion that the subject was too inebriated to drive. In other words, the FSTs were hardly more accurate at predicting intoxication than flipping a coin.