A Florida Validation Study of the Standardized Field Sobriety Test (S.F.S.T.) Battery

A Florida Validation Study of the Standardized Field Sobriety Test (S.F.S.T.) Battery

This research project was prepared for the State Safety Office, Department of Transportation, State of Florida in cooperation with the National Highway Traffic Safety Administration, U.S. Department of Transportation and/or Federal Highway (under project number AL-97-05-14-01). The conclusions and opinions expressed in these reports are those of the subgrantee and do not necessarily represent those of the State of Florida, Department of Transportation, State Safety Office, the U.S. Department of Transportation or any other agency of the State or Federal Government


Institute of Police Technology and Management
University of North Florida

Director Russell Arend, Contractor

Pinellas County Sheriff's Office

Sergeant Teresa R. Dioquino, Project Manager

Southern California Research Institute

Marcelline Burns, Ph.D. Investigator

Dary Fiorentino, M.A. Graphics Consultant

Theresa Brown Senior Data Processor

Shana Gguyen Data Processor

Cindy Seymour Data Processor


During the years 1975 - 1981, a battery of field sobriety tests was developed under funding by the National Highway Traffic Safety Administration (NHTSA), U.S. Department of Transportation (Bums and Moskowitz, 1977; Tharp Burns, and Moskowitz, 1981). The tests include Walk-and-Turn (WAT), One-Leg Stand (OLS), and Horizontal Gaze Nystagmus (HGN). NHTSA subsequently developed a training curriculum for the three-test battery , and initiated training programs nationwide. Traffic officers in all 50 states now have been trained to administer the Standardized Field Sobriety Tests (SFST's) to individuals suspected of impaired driving and to score their performance of the tests.

At the time the SFST's were developed , the statutory blood alcohol concentration (BAC) for driving was 0.10% throughout the United States. The limit now has been lowered in a number of states to 0.08% for the general driving population. "Zero tolerance" is in effect in some jurisdictions for drivers under age 21, and commercial drivers risk losing their licenses at a BAC of 0.04%. It is likely that additional states will enact stricter statutory limits for driving. In light of these changes, a re-examination of the battery was undertaken by McKnight eta!. (1995). They reported that the test battery is valid for detection of low BAC's and that no other measures or observations offer greater validity for BAC's of 0.08% and higher.

The three tests have been incorporated into Drug Influence Evaluations (DIE's) which are conducted by certified Drug Recognition Experts (DRE's) whenever an individual is suspected of being drug-impaired. As part of a DRE evaluation, the SFST's provide important evidence of drug impairment and contribute to the DRE's three-part opinion:

  • Is the individual impaired by a drug or drugs?
  •   If yes, is the impairment drug-related?
  • If yes, what category or categories of drug account for the impairment?

A study was conducted in Colorado to examine the validity of the SFST's when used by experienced officers in the field (Burns and Anderson, 1995). The design of the study insured that roadside testing was limited to the three-test battery, and that officers' decisions were not influenced either by the driver's performance of other behavioral tests or by measurement of BAC with a preliminary breath tester (PBT). The obtained data demonstrated that more than 90% of the officers' decisions to arrest drivers were confirmed by analysis of breath and blood specimens.

A recently reported NHTSA funded study was conducted by Anacapa Sciences, Inc. in collaboration with the San Diego Police Department to examine the validity of the SFST's for both 0.08% and 0.04% (Stuster and Bums, 1997). Officers' estimates of whether a driver's BAC was above or below 0.08% or 0.04% were found to be more than 90% correct.

The Colorado and California studies provide relevant and current field data. The validity of the tests when they are administered in the context of drug evaluations was examined in a retrospective analysis of the records of the Phoenix DRE Unit (Adler and Burns, 1994). It was found that a suspect's performance of the tests provides valid cues of drug impairment. The study reported here was conducted in collaboration with the Pinellas County Sheriffs Office (PCSO) and expands the examination of the SFST's to the State of Florida. An overview of PCSO and the demographics for Pinellas County can be found in Appendix I


During the early years of SFST use by law enforcement, legal challenges were relatively infrequent. For more than a decade now , however, defense counsel in many jurisdictions has sought to prevent the admission of testimony about a defendant's performance of the three tests. The objections, which continue to be persistent and vigorous in 1997, typically focus on test validity and reliability as demonstrated in the original laboratory research. It is entirely appropriate to inquire whether that early research to identify a best set of sobriety tests was conducted with scientific rigor. Beyond that inquiry, however, the data , which were obtained in a laboratory setting and now are more than twenty years old, are of little interest. Certainly, they are only marginally relevant to current roadside use of the tests. The question which begs to be addressed in 1997 is whether the tests are valid and reliable indices of the presence of alcohol when they are used at roadside under present day traffic and law enforcement conditions.

Experience and confidence have a direct bearing on an officer's skill with roadside tests. In this regard, note that the officers who participated in the early SCRI studies had been only recently and briefly (4 hrs) trained to administer the test battery. There had been no time for them to use the tests in the field where they might have developed confidence in decisions based on them. Nonetheless, their decisions were 76% correct in the first study and 81 % correct in the second study.

At this point in time, many traffic officers have had ten or more years' experience with the test battery and many report that they confidently rely on them. Since it seems unlikely in the extreme that they would continue to rely on tests which repeatedly lead to decision errors, it is a reasonable assumption that more often than not their roadside decisions to arrest are supported by measured BAC's. Whether their decisions to release are correct is largely unknown since the released driver's BAC generally is not measured.

Traffic officers are charged with the detection and arrest of impaired drivers. Although their roadside duties are central to roadway safety, recognition of alcohol impaired drivers can be difficult and is, therefore, subject to error. If officers are to effectively meet this particular enforcement responsibility, they need to augment their general observations of suspects with sensitive, accurate sobriety tests. The tests not only aid in the removal of dangerously impaired drivers from the roadway, they also protect the driver who is not alcohol or drug impaired from being' improperly detained. Thus, rigorous examinations of the SFST's are important to traffic safety.

Whether an officer's decision about a suspected DUI driver is correct or incorrect is determined by measurement of BAC and the jurisdiction's statute. The Florida statute (Appendix II) states that a person is guilty of driving under the influence of alcohol if he (1) "has a blood alcohol level of 0.08 or more grams of alcohol per 100 milliliters of blood" or the equivalent measure "a breath alcohol level of 0.08 or more grams of alcohol per 210 liters of breath". In commonly used nomenclature, a driver in the State of Florida is subject to arrest if he is operating a motor vehicle when his BAC is 0.08% or higher.

Roadside decisions may be correct or incorrect, each under two different circumstances as illustrated in Figure 1. An arrest is "correct" and is tallied in Cell 1 when a breath test confirms that the suspects BAC is at or above the statutory limit of 0.08%. Similarly, a release is "correct' and is tallied in Cell 4 when the driver's BAC is below 0.08%. An incorrect arrest has occurred if the BAC of a driver taken into custody for DUI is found to be less than 0.08% (Cell 3). An incorrect release has occurred if the released driver's BAC is equal to or greater than 0.08% (Cell 2). In this context, the cell labels "Correct" and "Incorrect" refer only to the BAC criterion, and an incorrect decision occurs when the measured BAC does not support the officer's decision. In the broader sense of impairment, the labels may or may not accurately reflect correctness or error. It is important to understand that a driver incorrectly arrested in terms of the BAC standard of 0.08% may have been dangerously impaired by a lower BAC or by some other drug or condition.

FIGURE 1 Decision Matrix      OFFICERS' DECISIONS 

Measured BAC Arrest Release
> 0.08% 1 Correct Arrest 2 Incorrect Release
<0.08%  3 Incorrect Arrest 4 Correct Release 

Decisions to arrest for DUI (Cells 1 and 3) can be readily evaluated. Unless a driver refuses to provide a specimen for BAC measurement, the question of accuracy is quickly resolved. Information typically is not available, however, to determine whether non-arrested drivers were correctly released. Because BAC data for released drivers are difficult to obtain, they rarely appear in assessments of officer performance, but a validation study of the SFST's requires information to fill all four cells of the matrix.

(1) In the interest of brevity and readability, the male gender will be used throughout this report. The authors expressly acknowledge, however, that many traffic officers are female and recognize that many impaired drivers are female.


The hypothesis of this study appears below.


Study Hypothesis

DUI arrest decisions made by Florida law enforcement officers

  •   who have been trained under NHTSA guidelines to administer, score, and interpret the Standardized Field Sobriety Tests (SFST's),
  •   who have developed experience and skill with the SFST's,
  • who use only the 3 test battery to examine suspected DUI drivers, and who do not have access to a preliminary breath tester (PBT)

will be > 90% correct, as confirmed by measured BAC's.

The design of the study was dictated by the need to insure:

  • standardization of SFST administration and interpretation,
  • data integrity, and
  • data completeness

The compromise of any of these requirements would have made interpretation of the obtained data both difficult and. subject to question.  Note that the study drivers were a subset drawn from the total population of drivers. The inclusion and exclusion criteria were determined by the primary study objective; i.e., an assessment of the accuracy of officers' arrest and release decisions based on the SFST's. Thus, throughout the study period, drivers on the roadways within Pinellas County (who were not involved in a traffic crash) were included in the study if 1) they were detained at roadside and 2) due to evidence of impairment they were asked to perform' the SFST's.

There undoubtedly were alcohol impaired drivers on Pinellas County roadways during the study period who entirely escaped detection. It is also possible that impaired drivers were stopped, but their impaired states were not recognized and they were not asked to perform the SFST's. That can occur when the driver is a chronic, heavy drinker who has developed a tolerance to the effects of alcohol and does not display obvious symptoms. Although these individuals are germane to an examination of DUI enforcement overall, they properly were not part of this study, which was strictly defined as a validation study of SFST's. It was limited to drivers who were asked to perform the tests.


A.  SFST Standardization

To examine the validity of the SFST's the study assessed the correctness of officers' arrest and release decisions, which were based on suspects' test performance. The proper execution of the study depended on the officers in the field. It was essential for them to strictly adhere to standardized testing since deviations in instructions and demonstrations would have yielded study findings only marginally relevant to standardized methods.

Participating officers were PCSO deputies with specialized training in DUI enforcement, including SFST training. They fully met all study criteria, and all were assigned to the PCSO Selective Traffic Enforcement Program (STEP). During a pre-study orientation and training session attended by deputies and observers, the study design and objectives were presented by the Study Investigator. The Project Manager, who is a certified SFST instructor, provided refresher training by reviewing and demonstrating standardized administration of the tests. Questions and comments from the individuals in attendance appeared to stem from genuine interest and commitment to the study objectives.

The deputies were asked to complete an Officer information form (Appendix III). The data obtained with the form have been used to rank the officers by years of law enforcement experience (Table 1). In Table 2 they are ranked by the estimates made by each deputy of the total number of DUI arrests he had made up to the time of the study.

TABLE 1 Participating Pinellas County Sheriff Deputies Ranked by Years of Law Enforcement Experience

Rank Badge  Years-Months-Service  Year SFST Training  # DUI Arrest Certification 
1  52626  Frank Fleming  19 yrs  1990  400  DUI Instructor /DRE
2  52610  Timothy W. PeleIla  10 yrs 6 mos  19880  250  DUI Instructor /DRE
3  53708  Eric J. Osborne  9 yrs 6 mos  1987  200  DUI Instructor /DRE
4  52864  Richard C. Nalven  9 yrs 4 mos  1988  340  DUI Instructor
5  52863  Howard E. Skaggs  9 yrs 3 mos  1988  430  DUI Instructor /DRE
6  53081  Tommy G.Craft  7 yrs 7 mos  1994  300  DUI Instructor
7  53241  Frank Arena  7 yrs 6 mos  1994  425  DUI Instructor
8  53478  Robert V. Hasmes  6 yrs 4 mos  1993  720  DUI Instructor

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