We have previously discussed how field sobriety tests work, and how police officers in Lansing and throughout Michigan use them to help build a case of DUI against a suspect. Unlike a blood test to measure the amount of alcohol in someone's system at a certain time, field sobriety tests are not scientifically objective. It is up to the police officer to decide whether someone has passed the tests or not. No matter how well officers are trained, mistakes or biases will inevitably color the process at least some of the time.
In addition to this flaw, the tests themselves are not easy for everyone to pass, even if they have not had a drop of alcohol. A TV channel in another state recently conducted an experiment not long ago. They had sober people perform three standard field sobriety tests at the direction of a local police officer.