Police officers in Indiana and around the country use a standardized field sobriety test developed by the National Highway Traffic Safety Administration in the 1980s to determine whether or not motorists are operating their vehicles while under the influence of alcohol. Blood, urine and breath tests are usually used to establish intoxication in court, while SFSTs are used by police officers in the field when they need probable cause to ask for a chemical test or make an arrest.
SFSTs are flawed
The results of SFSTs are rarely used in court in impaired cases because their results are subjective. Studies have found that STSTs are only reliable about 80% to 90% of the time, which means their results cannot prove intoxication beyond reasonable doubt. Prosecutors are also reluctant to enter SFST results in court because police officers often deviate from the NHTSA procedure by asking drivers to perform tasks like reciting the alphabet backward.
Age and medical conditions
The body deteriorates as we grow older no matter how nutritious our diets are or how much we exercise. Many older people would have difficulty completing the walk and turn and one-leg stand tests even while completely sober, and so would motorists who suffer from medical conditions that affect equilibrium and balance. Even the NHTSA concedes that field sobriety tests are not very reliable when the people who take them are over the age of 65 or suffer from inner ear or back problems.
Probable cause
Police officers use STSTs to find probable cause rather than evidence, so their results could lead to an arrest but would probably not be used in court. If a prosecutor did decide to introduce the results of a SFST during a trial, the defendant would have several ways to challenge the results. They could cite studies that reveal how unreliable STSTs are, they could question the actions or judgement of the police officer involved, or they could argue that they were placed in an unfair position due to their age or health.