Field Sobriety Test History

The Studies That "Validated" The Exercises

Field sobriety tests(also called "roadsides" or "physical sobriety exercises"or “FST’s”) are used by the police during their DUI investigations.  These exercises attempt to measure impairment.  A DUI suspect's performance is used during the officer's evaluation of whether enough probable cause exists to arrest.  The problems with these exercises are abundant.  Even when performed correctly under proper conditions, they are not reliable indicators of impairment, as many other factors other than intoxication could explain poor performance.  Moreover, they are often improperly administered in the field by poorly trained police officers who are not qualified to interpret the results.

To help ensure the roadside exercises are administered uniformly, the National Highway Traffic Safety Administration (NHTSA) publishes guidelines that they recommend police agencies to use while training their officers. NHTSA’s recommendations are based upon research studies that have been conducted on the different exercises and their reliability in detecting impairment.  As explained in other sections, several exercises and their variations are still administered despite NHTSA's recommendations that only the Walk &Turn, HGN, and One-Leg Stand should be used for detecting impairment. Research has indicated that the other exercises are too unreliable for accurately measuring intoxication.

NHTSA relies on the six major studies that have been conducted for their recommendations.  Each study is listed and explained below:

1.  The “Florida” Study

A Florida Validation Study of the Standardized Field Sobriety Tests (S.F.S.T.) Battery, by Marcelline Burns, Ph.D. (1997).

This study is the most recent study of the six.  For a period of 3 months, eight officers were observed as they conducted DUI investigations.  A total of 379 drivers were stopped, but only 256 could be used in the study.  The others were not used because they either refused to submit to the FST’s or the breath test, or because they were released without being administered them.  The results of each DUI suspect’s field sobriety tests were compared to the results of a later administered breath test to gauge how accurately the police were estimating BAC levels based on evaluations of sobriety exercise performance.

Out of 256 people, nine were improperly arrested (4 of which blew under a .05) and nine were improperly released (they “passed” the sobriety exercises but “failed” a subsequent breath test).  Those that were improperly released submitted to a breath test after being promised if they “failed” they wouldn’t be arrested (unless they got back in their car and drove).  Dr. Burns concluded that when properly administered, the field sobriety exercises may indeed be reliable indicators of impairment. She also concluded that “If it can be shown that officers’ reliance on the tests is misplaced, causing them frequently to err, then the officers, the courts, and the driving public need to be aware that the tests are not valid and that DUI laws are not being properly enforced.

2.  The San Diego Study

Validation of the Standardized Field Sobriety Test Battery at BACs Below .10 Percent, by Jack Stuster and Marcelline Burns (1998).

Seven police officers from a San Diego police department participated in this study that not only sought to compare field sobriety test results to the results of subsequently administered breath tests, but also attempted to measure the ability of the officers to accurately estimate BAC levels in DUI suspects.  Only experienced and well-trained officers were allowed to participate in the study, suggesting that inexperienced and untrained officers will not produce as accurate estimations as experienced officers would.  The study found HGN to be the most “effective” sobriety exercise for estimating BAC levels.

Only 297 people were measured in the study.  Each individual was administered the“standard” three battery physical sobriety exercises (the Walk & Turn, H.G.N., and the One-Leg stand), after which the officer was to record his estimation of what he thought the suspects’ BAC level was.  Then a portable breath test (PBT) was administered and the results were recorded.  Nine of the 297 people were improperly estimated to be DUI – subsequent PBT results confirmed that the officers incorrectly thought their BAC level was higher than.08.

There were several problems with the way this study was conducted.  First, the officers were poorly supervised.   Thus there is no way to tell whether their BAC estimations were properly recorded before the breath test was given.  Furthermore, people who were over .08 but within the margin of error of the breath test were not mentioned, even though those that blew under.08, but within the margin, were. Two significant findings were made that are relevant for defense purposes:

• “It is unlikely that complex human performance, such as that required to safely drive an automobile, can be measured at roadside…The link between BAC and driving impairment is a separate issue, involving entirely different research methods”.

• “Horizontal Gaze Nystagmus lacks face validity because it does not appear to be linked to the requirements of driving a motor vehicle.  The reasoning is correct, but it is based on the incorrect assumption that field sobriety tests are designed to measure driving impairment.”

3.  The Colorado Study

A Colorado Validation Study of the Standardized Field Sobriety Test (SFST)Battery, by Ellen Anderson and Marcelline Burns (1995).

This study is unique and unlike the others because both the weather and the laws in Colorado differ significantly from other states where studies have been conducted. In Colorado, instead of a .08 per se DUI law, there are two possible violations - .10 DUI and .05 DWAI. Unlike the other studies, the officer’s estimation was based on a .05 intoxication standard instead of a .08.  Thus the results of the study tell us little to nothing about the reliability of an officer’s estimated measure of .08 BAC levels using field sobriety tests.

Only 234 subjects were evaluated and given the “standard” three battery field sobriety exercises.  The Colorado officers were not equipped with portable breath tests.  Problems with this study were lack of supervision, and bias observations made by people that were affiliated with the police department and/or participants of the study.  Officers reported only errors that were “relatively minor in nature.”

Women made up only a small percentage of the subjects that were tested (18%).  38% of incorrect releases were women, and women made up 25% of the incorrect arrests.  The study found that many clues for the HGN exercise may occur at low BAC levels for certain people but not others.

Overall, the study claims to have found evidence that the field sobriety tests, when administered by experienced and well trained officers, are “valid indices of the presence of alcohol.”  The study claims that officers were correct in assessing whether someone should be released or arrested 86% of the time, with 93% of their arrest decisions accurate. While this study is more organized and thorough then other studies, keep in mind that it measures officers' ability to estimate impairment of a .05 level.  Thus it does not help determine how reliable the exercises are in estimating impairment at a .08 level.

4.  The Field Evaluation Study

Field Evaluation of a Behavioral Test Battery for DWI, by Theodore E. Anderson, Robert M.Schweitz, and Monroe B. Snyder, (1983).

This was a small study conducted over a three month period.  Police agencies from four jurisdictions in North Carolina, Virginia, Maryland and Washington D.C. were used.  The study aimed to evaluate reliable how the H.G.N, One-Leg Stand, and Walk & Turn were.

The accuracy of the study was a major issue, as the officers were not supervised and received only one day’s worth of training in the administration of the exercises.  Furthermore, since the officers were equipped with PBTs, even subjects who “passed” the sobriety tests but subsequently “failed” a breath test were arrested.  Furthermore, each subject was stopped specifically because they were suspected of DUI, because their driving pattern indicated impairment before any police contact with the subject was actually made.  Thus the police were more likely to be bias and the results skewed, since the officer was already suspecting impairment before a stop was even made.

The study claims that the police were 83% accurate in their ability to detect impairment solely based off FST results.  However, of those that were incorrectly classified, 16% were falsely estimated to have a BAC level of .10 or more.

5.  Development & Field Test ofPsychophysical Tests for DWI Arrests

Development& Field Test of Psychophysical Tests for DWI Arrests,by V. Tharp, Marcelline Burns, and Herbert Moskowitz (1981).

Of all six major studies conducted on the topic of field sobriety exercises, this is the most significant.  Its results have been quoted by every NHTSA manual to date.  10 officers from different LA police agencies assessed 297 volunteers that drank in the lab from .00 BAC to .18.  Of the 297 volunteers, 202 were male and only 95 were female.  One female had to leave the study early because she became ill.  Every participant was over the age of 21.  Only two people were over the age of 65.  Although each person was instructed not to eat, drink, or take drugs prior to arriving at the lab, three people showed up with a BAC of .05 or more.  No chemical testing was done on any subject to rule out drug use.  Instead, subjects were administered the HGN to rule out potential drug users.

The police were able to accurately classify 81% of the participants as below or above a .10 BAC level.  The results of the study are as follows:

6.  The 1977 Study

Psychophysical Tests for DWI Arrests, Marcelline Burns and Herbert Moskowitz (1977),

This was the original study done on FSTs.  It was specifically performed for NHTSA, and lasted for a 20 month period from June 1975 to February 1977.  A total of 238 people participated in the study, all whom were heavy, moderate, or light drinkers. Of the 238 people,only 70 were women.  Ages ranged from 20years old to 70 years old.  Ten police officers administered six field sobriety tests on subjects with BAC levels ranging from .00 to .150 (those with .00 were given placebo drinks).  The exercises given included the Walk &Turn, the One-Leg Stand, Alcohol Gaze Nystagmus, Romberg balance, subtraction,Counting Backward, and Letter Cancellation.

The study found that officers were able to correctly estimate whether someone should be arrested 76% of the time.  The police correctly released suspects 73% of the time.  Even though 6 people were not given any alcohol at all, the offices said they would have arrested them.  The findings indicated that the most reliable exercises are the Walk & Turn, One-Leg Stand, and the Alcohol Gaze Nystagmus.  The study also purported to show that impairment could occur below .10, and indeed the authors encourage a nationwide limit of .08, which they feel is “more appropriate.”

The problems with the reliability of the study are abundant.  First, although the subjects were instructed not to eat or use any drugs or alcohol before coming in, some subjects did not follow instructions.  A few people even showed up with elevated BAC levels.  The research findings did not take these problems into account.  The results of the field sobriety exercises were only compared to subsequently obtained BAC test results - never at any time was any test result compared with a person's actual ability to operate a motor vehicle.