The field sobriety tests are only reliable to a certain extent. In every test, there must be constants to compare results so the individual can pass or fail. The varying factors that could influence the reliability of an FST include the individual being tested and the officer administering them.

The main problem arises where there is no scientific standard for establishing impairment based on the amount of THC in the body. THC is the main component of pot that gets users "high". The drug is metabolized very quickly, but remains in the body for a long time in fat cells, well after the high wears off.

The police use three types of field sobriety tests to decide whether they have probable cause to arrest a suspect they pull over for DUI. Legal experts advise...