San Diego Criminal Lawyers Blog
What Exactly is a Polygraph Test?
In tv shows and movies, polygraphs (or “lie detector tests”) are often painted as mechanisms by which a defendant “gets off” or proves his or her innocence. Polygraphs are machines that hook up to a person to measure their physiological indicators such as perspiration and heart rate. It was once thought that when a person tells a lie, their heart rate and blood pressure change to indicate so. However, what many people do not know, is that polygraph tests are generally unreliable (ie. there are “false positives” or negatives), and their use has decreased. For example, if a person is nervous simply by virtue of taking a lie detector test, their heart rate will increase regardless and their test results will be inconclusive, rather than “passing.” Polygraphs may also be fooled if one is just able to control their physiological responses.
Rules on Polygraphs
Once arrested, in no state can anyone be forced by the police to take a polygraph test; it may only be voluntary. Most people are unaware of this, and succumb to the psychological pressure that a suspect who is innocent has “nothing to lose” should s/he take a lie detector test.
However, once taken, states differ as to the admissibility of the polygraph results in court. Some states such as New York and Texas ban the use of polygraph results as evidence, while other states allow the use of polygraph tests based on certain conditions. Specifically, the U.S. Supreme Court in Daubert v. Merrell Dow Pharmaceuticals (1993), detailed how courts deal with polygraph tests as scientific evidence, since neither the U.S. Code nor the Federal Rules of Evidence specifically addresses the admissibility of polygraph results in Court. Essentially, the Supreme Court made it an individual judge’s decision to decide whether to allow polygraph results, so each court can decide differently. Each judge must take into consideration several factors: 1) whether the theory or technique can be and has been tested, (2) whether it has been subjected to peer review, (3) whether it has a high known or potential rate of error, and (4) whether the theory has gained general acceptance within the scientific community.
In the state of California, both sides have to agree for anyone to take a polygraph. In criminal cases in California, in addition to both sides having to agree for anyone to take a polygraph, both the prosecution and defense must also agree for the results of the polygraph test to be admitted at trial or in any criminal proceedings (California evidence code 351.1). Even if a defendant agrees to voluntarily take the test, the results of the test are not admissible in evidence in California criminal courts (unless it was agreed by both parties that results are admissible), but the statements he made at the time of the test are admissible.
San Diego Criminal Lawyer
If you are being pressured to take a polygraph test or are considering volunteering for one, please call the Law Offices of David Boertjie and ask for a free consultation. We are here to advise you of your rights and give you insight on what you should do for your specific situation.