Category Archives: Field Sobriety Tests

Circadian Rhythm and Field Sobriety Tests

Most drunk driving arrests take place at night, often well after midnight. One reason for this is that many police officers engage in "cherry picking" — that is, the illegal practice of staking out bars and restaurants from about 10:00pm to "closing time" at around 2:00am, pulling cars over on some pretext as patrons leave and drive away.

It is during this period of time that the individual’s circadian rhythm is taking effect. This is the 24-hour biological alarm clock in each of our bodies, often noticeable when we experience "jet lag".

Researchers have found that individuals will perform more poorly in tests during the low point of the circadian rhythm — that is, during the hours after midnight and into the early morning.

Unfortunately, it is just such tests — called "field sobriety tests" — that officers use to determine whether a driver is intoxicated or not.

British physicians and psychiatrists reported that "the same blood alcohol level is associated with a significantly greater impairment of different aspects of psychological funtioning when achieved in the morning." "Circadian Variation in Effects of Ethanol in Man", 18 (Supp. 1) Pharmacology, Biochemistry and Behavior 555.

The researchers concluded that "the differences we have found (in field sobriety test performances)…must be attributable to circadian change and susceptibility of the body to its effect."

The “Nystagmus” Field Sobriety Test: A Fraud?

The critical part of any drunk driving investigation is the administration of the "field sobriety tests" (FSTs).  These usually consist of a battery of excercises involving balance, coordination and mental agility — and are difficult to perform for even a sober person under ideal conditions (see "Field Sobriety Tests: Designed for Failure?"). 

Although there are many different tests (finger-to-nose, alphabet, etc.), an increasing number of law enforcement agencies are requiring their officers to use only the federally-recommended battery of three "standardized" FSTs.  The most recently developed of these is horizontal gaze nystagmus (HGN), commonly known as the "eye test".  It is particularly effective in trial not because of its accuracy, but rather because it appears to jurors as scientific in nature.

As I have indicated in previous posts, however, HGN as a test for intoxication is fundamentally flawed and rarely understood or properly administered by police officers.  (See "Nystagmus: The Eye Test", "Nystagmus: The Eye Test (Part 2)", and "Nystagmus: The Eye Test (Part 3)".)

A scientific study (144(3) Science and Justice 133-139) has investigated the scientific validity of the nystagmus test:

The Horizontal Gaze Nystagmus (HGN) test was conceived, 
developed and promulgated as a simple procedure for the determination of the blood alcohol concentration of drivers suspected of driving while intoxicated (DWI). Bypassing the usual scientific review process and touted through the good offices of the federal agency responsible for traffic safety, it was rushed into use as a law enforcement procedure, and was soon adopted and protected from scientific criticism by courts throughout the United States. In fact, research findings, training manuals and other relevant documents were often held as secrets by the state. Still, the protective certification of its practitioners and the immunity afforded by judicial notice failed to silence all the critics of this deeply flawed procedure….

In 1998 the integrity of the statistical evaluation of the original research upon which the validity of the tests rested was unfavorably reviewed [5]. In 2001 new research indicated that the Horizontal Gaze Nystagmus (HGN), the cornerstone of the test battery was fundamentally flawed and that the HGN test was improperly conducted by more than 95% of the police officers who used it to examine drivers suspected of driving while intoxicated (DWI) [6]. This summary critique demonstrates that it is scientifically meretricious and that the United States Department of Transportation indulged in deliberate fraud in order to mislead the law enforcement and legal communities into believing the test was scientifically meritorious and overvaluing its worth in the context of criminal evidence….

"Deliberate fraud".  Pretty strong language for a scientific journal.  After reviewing the flawed and deceptive justifications for using nystagmus in DUI investigations, the researchers concluded that the test was essentially without scientific validity.

The state’s argument for the field sobriety tests does not rest on 
proof of merit, but upon 
qui tacet consentit reasoning that those tests have been so widely accepted they must have been subjected to some kind of review prior to adoption in the many jurisdictions where they are used, that somewhere along the way someone would have spotted the flaws and shortcomings. Considering that the student manual was originally considered to be a confidential state document and was only obtained through an Open Records Act request, silence from the scientific community cannot be considered an endorsement of the program.

Blood-Alcohol Level When Tested vs When Driving

It is illegal to have a blood-alcohol concentration (BAC) of .08% or greater while driving a vehicle. It is not illegal to have a BAC of .08% or greater while blowing into a breathalyzer in a police station. In other words, just because a breath test shows a level of, say, .09%, it does not mean that the BAC when the suspect was driving an hour earlier was .09%.

So what was the breath alcohol level when driving?

Well, we’ll never know: There is no evidence of the BAC at the time of actual driving. However, we can be fairly sure that it wasn’t .09%, since the body is constantly either absorbing or eliminating alcohol and the BAC is therefore constantly rising or falling. If it was falling, then we can expect the BAC when driving was higher — .10% or more. But if it was rising…..

Let’s take a typical example. The subject — let’s call her “Janet” — finishes dinner by throwing down “one for the road”, a 12-ounce can of beer containing .05% alcohol. She is stopped by an officer soon after leaving the restaurant, alcohol is smelled on her breath and she is given field sobriety tests. She does marginally well but, to be sure, the officer takes her into the police station for breath testing. About 45 minutes after drinking the alcohol, Janet breathes into the breathalyzer. The result: .09%. She is booked and his driver’s license confiscated.

It will take, on average, about one hour for the alcohol to be absorbed and reach peak levels of concentration in the blood, thereafter to be eliminated from the body. This is only an average; it can vary from 15 minutes to 2 hours; some invidividuals can reach peak concentration ten times faster than others. Dubowski, “”Absorption, Distribution and Elimination of Alcohol: Highway Safety Aspects”, Journal on Studies of Alcohol, Supp. 10 (July 1985). This makes trying to estimate earlier BAC levels no better than a rough guess, and scientists have unifromly condemned the practice. See, for example, “Breath Alcohol Analysis: Uses, Methods and Some Forensic Problems”, 21 Journal of Forensic Sciences 9.

Applying averages to Janet, though, we can expect the last drink to have had little if any effect on her blood-alcohol concentration while she was driving. By the time she is being tested at the station 45 minutes later, however, she is reaching peak concentration. In other words, Janet’s BAC has been rising. At about 120 pounds, we can estimate (read “guess”) that the can of beer has increased her BAC by about .031%.

Translation: the breathalyzer reading of .09% at the station indicates a BAC while driving of only .06%. She is not guilty. But the “evidence” will convict her.

Just to make things worse….As I indicated, attempts to guess BACs when driving earlier than when tested have been condemned by scientists. This makes things tough for prosecutors. Solution? As I discussed in an earlier post, “Whatever Happened to the Presumption of Innocence?”, most states today have passed laws — directly contrary to scientific truth — which presume that the BAC at the time of being tested is the same as at the time of driving!

In other words, unless the defendant can prove that his BAC was different than when tested, the jury will be instructed that they must find that it is the same. In effect, the defendant is presumed guilty. And since there is no evidence of the BAC when driving, there is no way for the defendant to rebut the presumption.

These laws do, however, make getting convictions much easier.

Field Sobriety Tests Found to be Inaccurate

Proponents of the so-called “standardized” field sobriety tests (SFSTs) have long pointed to federally-funded field studies which indicate a high correlation between performance on the tests and actual blood alcohol concentrations (BAC). 

Subsequent studies, however, have called those conclusions into question.

Originally, the National Highway Traffic Safety Administration (NHTSA) paid a private group, the Southern California Research Institute, to conduct studies to find which among the various field sobriety tests used by police were most effective and to develop a standardized 3-test battery.  SCRI subsequently reported to NHTSA that a battery of walk-and-turn, one-leg-stand and nystagmus provided a strong correlation with breath test results.

Confronted with questions about those conclusions, NHTSA later commissioned the same researcher who had conducted the original studies, Marcelline Burns, to  corroborate the accuracy of her own tests of the SFSTs – rather than commission an independent source. 

Burns accompanied a small number of San Diego officers conducting actual DUI investigations in the field.  After administering the SFSTs, the officers were asked to guess whether suspects had blood alcohol  concentrations (BAC) over or under .08%.   Burns reported a 91% correlation between SFSTs and BAC over-under estimates, thereby validating the battery of tests she had helped create.

A subsequent scientific article challenged Burns’ corroboration of her own research.  In Hlastala, Polissar and Oberman, “Statistical Evaluation of Standardized Field Sobriety Tests”, 50(3) Journal of Forensic Sciences 1 (May 2005), the raw data used in the validation study were obtained from NHTSA through the Freedom of Information Act.  The methodology used was then reviewed and the data subjected to statistical analysis.

The methodology was found to be seriously flawed in a number of respects.  For one thing, many of the suspects had very high BACs, making estimates of whether a suspect was over .08% obvious regardless of SFST performance.  For another, there was no attempt to isolate the influence of SFST performance from other factors:  officers estimated BACs after the field sobriety tests, but they also took into account earlier observations, such as erratic driving, slurred speech, odor of alcohol, flushed face, admissions as to amount of alcohol consumed, etc.

The most glaring defect in Burns’ corroborative study was that “all police officers  participating in the study were equipped with NHTSA-approved portable breath testing devices”.  In other words, the San Diego officers already had the results of portable breath tests before they were asked to estimate the BACs later obtained at the station!

After reviewing the flawed methodology, the raw data was then statistically analyzed.  The conclusions:

If we consider three ranges of MBAC [measured blood alcohol content], 0.00% to 0.04%, 0.04% to 0.08%, and 0.08% to 0.12%, the officers’ EBAC [estimated blood alcohol content] overestimated the MBAC 76%, 67% and 48% of the time, and underestimated it 14%, 26% and 28% of the time. 

In other words, officers relying upon field sobriety tests were far more likely to overestimate  BACs than underestimate — particularly with those suspects having very low BACs. 

(T)he utility of the SFST depends very much on how intoxicated an individual is.  Accuracy (and specificity) are low when individuals are close to 0.08% MBAC, but if the individuals are quite intoxicated, such as above 0.12%, then accuracy is high.

In borderline cases involving persons at or under the legal limit, then, officers were very poor at estimating blood-alcohol levels based upon SFSTs.  And it is these cases, of course, that are critical.  Suspects with high BACs are relatively easy to single out without the help of field tests; it is for the closer cases, particularly those who are innocent (below .08%), that the SFSTs are designed.  And it is with these very cases that the tests apparently fail. 

Put another way, accuracy in using field sobriety tests is high when they are not needed — and low when they are.

For another independent study conducted by Professor Spurgeon Cole of Clemson University, in which he found field sobriety tests to be worthless, see Are Field Sobriety Tests Designed for Failure?.

Field Sobriety Tests “Unreliable” for Older Drivers

In just another example of law enforcement's one-size-fits-all approach to drunk driving cases, Dr. Lance L. Gooberman, M.D., offers the following comments:

The National Highway Traffic Safety Administration, based upon studies done in 1977 and 1983, determined that standardized field sobriety tests were unreliable in those over age 60. This is reflected in the National Highway Traffic Safety Administration manual from 1991. In 2006 it was changed to age 65, however, this was not based upon any additional data.

A recent British study indicates that the breakpoint for reliability on field sobriety tests is the age of 40.   Dixon, Clark and Tiplady, Evaluation of a Road Side Impairment Test Device Using Alcohol, 41 Accident Analysis and Prevention, 412-418 (2009). This is more consistent from a medical perspective. Therefore, field sobriety tests cannot be relied upon in people greater than 40 years of age.

For further examples of the "one-size-fits-all" road to conviction, particularly with blood and breath alcohol analysis, see my earlier post Guilty…of Not Being Average?