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Standardized Field Sobriety Tests

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Definition - What does Standardized Field Sobriety Tests mean?

Although a wide variety of field sobriety tests have been used throughout history to help law enforcement officers across the United States detect drunken drivers, the National Highway Traffic Safety Administration (NHTSA), with assistance from the Southern California Research Institute, have established through testing, what they consider to be the three most effective field sobriety tests.

The Standardized Field Sobriety Test (SFST) has been formalized by the NHTSA and a formal program of training has been created to help law enforcement officers become more skillful at detecting DUI suspects. Standardization of field sobriety tests has also helped increase the ability of officers to present testimony in court of the behavior of the suspects. Currently formal administration and accreditation of the SFST training program is provided through the International Association of Chiefs of Police (IACP).

The Standardized Field Sobriety Test includes the following battery of tests:

  • Horizontal Gaze Nystagmus (HGN)- The HGN test measures the involuntary jerking of a suspect's eye which occurs naturally as the suspect gazes from side to side. This natural occurrence of nystagmus is exaggerated in drivers who have consumed large quantities of alcohol and can be detected when the eyes are rotated at lesser angles than a non-intoxicated driver. The HGN test can also identify drivers who are impaired by alcohol and unable to smoothly track an object as it is moved slowly horizontally in front of their eyes. The three indicators of impairment which a law enforcement officer is examining while performing the horizontal gaze nystagmus test are: 1) whether the driver can follow the object smoothly; 2) whether the driver's eye jerks distinctly at maximum deviation; 3) whether the onset of the eye's jerking is within 45 degrees of center.
  • Walk-and-Turn (WAT) - The walk-and-turn test is a divided attention test that should not be difficult for non-intoxicated drivers to perform. Not only must the driver listen, follow instructions and perform physical movements, but the driver must also be able to focus on mental and physical activities simultaneously (a skill frequently needed for driving). For the walk-and-turn test the driver must walk heel to toe down a straight line for nine steps, turn on one foot and return down the same line. Evidence of impairment can include stepping off the line, using arms for balance, taking the wrong number of steps, not following directions, not stepping heel-to-toe and stopping while walking.
  • One-Leg Stand (OLS) - The one-leg-stand test is also a divided attention test which will require the suspect to perform physical and mental tasks simultaneously. For this test the driver must stand with one leg raised off the ground approximately six inches and count aloud for approximately 30 seconds. Evidence of impairment during the one-leg-test can include swaying while balancing, using arms to balance, putting a foot down too early and hopping to maintain balance.

Though widely used by law enforcement officers throughout the United States, the Standardized Field Sobriety Test is still controversial. The National Highway Traffic Safety Administration maintains that "when the component tests of the SFST battery are combined, officers are accurate in 91 percent of cases, overall, and in 94 percent of cases if explanations for some of the false positives are accepted (Stuster and Burns, 1998)". Varying accuracy rates for the Standardized Field Sobriety Test have been produced in other studies.

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