Polygraphs as Truth or Lies

Thanks to the abundance of police dramas on television, people have begun to believe that a polygraph test is infallible. Many studies, as well as a Supreme Court case, have since revealed that the veracity of polygraphs is far from impeccable. Also, there are few if any credible sources that support the veracity of polygraph machines. As Dr. Saxe and Israeli psychologist Gershon Ben-Shahar (1999) notes, "it may, in fact, be impossible to conduct a proper validity study." In real-world situations, it's very difficult to know what the truth is.” (American Psychological Association [APA], 2004) Polygraphs do not function as a lie detector. A polygraph only directly measures the autonomic responses of the subject. It measures reactions such as changes in skin conductance, pulse rate, blood pressure, and breathing while the subject is asked a series of questions. From that data, it makes an indirect assumption that positive physiological responsive indicate dishonesty and vice versa. When taking a polygraph test, proctors use several different tactics to elicit responses from their subjects. One is called the "relevant-irrelevant" technique, which mixes questions like "Did you steal the money?" in with questions like "Is today Tuesday?" Questions that are relevant to the topic are suppose to cause a jump within the subject’s autonomic system and in turn would produce results on the polygraph. Another tactic that is commonly used is "comparison questions" this process is similar to relevant-irrelevant questioning except all of the questions pertain to the subject at hand (APA, 2004). For example, in a sex-crime investigation a suspect might be asked embarrassing control questions such as "Have you ever committed a sexual act you were ashamed of?" along with questions pertaining more directly to the case. The idea here is that the innocent person has a greater response to the control questions, dues to embarrassment or some other form of stress, whereas the guilty person will show a greater response to the case specific questions. (APA, 2004)
All of these strategies present some sort of bias or inaccuracy. For example, these "relevant-irrelevant" tactic produces false positives due to the fact that the innocent party can be caught off guard by the abrupt topic change and experience stress symptoms similar to those who were lying. There are many other factors that can cause false results on a polygraph. Things like subject interview interactions, level of anxiety, and the placebo effect. Even simple things like medication or even whether or not you have eaten that day can all obscure the results. The true accuracy of a polygraph test has always been questioned. In 2003 the NSA took on the most comprehensive analysis in the accuracy of polygraph tests. Their tests revealed some interesting findings.
In populations of examinees such as those represented in the polygraph research literature, untrained in countermeasures, specific-incident polygraph tests can discriminate lying from truth telling at rates well above chance, though well below perfection (Committee to Review the Scientific Evidence on the Polygraph, 2003).
Their analysis of the 30 most recent polygraph data sets showed an overall accuracy of 85 percent, and an analysis of seven field studies involving specific incidents showed a median accuracy of 89 percent. After looking at the data collected from the study, the NSA concluded that for screening individuals the margin of error for polygraph tests are too high. There are several factors that could be attributing to the inaccuracies. One may be the standard of the test, the criteria for determining a lie cannot be too strict so that it excludes guilty parties. Also, the criteria cannot be too loose that you receive too many false positive results. (Committee to Review the Scientific Evidence on the Polygraph, 2003). Despite the substantial evidence disproving polygraph tests there is a majority who still believes that they should remain a pertinent tool for determining message veracity.

References
Committee to Review the Scientific Evidence on the Polygraph; Board on Behavioral, Cognitive, and Sensory Sciences (BBCSS); Committee on National Statistics (CNSTAT); Division of Behavioral and Social Sciences and Education (DBASSE); National Research Council (n.d.) (2003). The polygraph and lie detection. Retrieved from http://www.nap.edu/openbook.php?isbn=0309084369
Ginton, A. (2013). A non-standard method for estimating accuracy of lie detection techniques demonstrated on a self-validating set of field polygraph examinations. Psychology, Crime & Law, 19(7), 577-594. doi:10.1080/1068316X.2012.656118
The Truth About Lie Detectors (aka Polygraph Tests). (August, 5th 2004). The polygraph and lie detection. Retrieved from http://www.apa.org/research/action/polygraph.aspx