However, there have been no empirical theories established to explain how a polygraph measures deception. For employee screening, the polygraph is used with current employees who may have committed acts prohibited by their employer or by law, but there is usually no specific known act that is the focus of the examination.
Some examiners believe that an important use of polygraph testing is in helping narrow the range of issues that need to be investigated, using both polygraph and other investigative tools. From the surveys on the use of the Event Knowledge Test new version of the Concealed Information Test for criminal investigation.
The polygraph examination, which includes the test and the interrogation surrounding it, is a tool for revealing truth. All of this behavior makes scientific analysis difficult. Meanwhile, a guilty subject is likely to be more worried about answering the relevant questions.
Accordingly, taking the test must remain voluntary, and its results must never be presented as conclusive.
Because this test format requires that the examiner have knowledge of the details of a specific event that is the topic of questioning, it cannot be used in typical security screening contexts. From to the present, at least six Americans have committed espionage while successfully passing polygraph tests.
From a scientific standpoint, these anecdotes are compelling indications that there is a phenomenon in need of explanation; they do not, however, demonstrate that the polygraph test is a valid indicator of deception.
Jacob Sdovnikruled that the polygraph has not been recognized as a reliable device.
The Polygraph and Lie Detection.