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 . 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) . 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.