Polygraph Testing is an indirect method because the person to be examined is not directly asked whether he has done this or that, but is asked whether he knows something about the act to be clarified. The goal is to find out if he has knowledge of the details of the crime that only the culprit can have. For this purpose, the person to be examined is first asked what he knows about the alleged act and where this knowledge comes from.
Then he is asked six questions on a particular aspect of the act (way of walking etc.), among which an alternative is the correct one. It has been shown that the reactions are particularly high when the question is answered in the negative answer true to the true answer.
Various laboratory studies even showed that “subjects without knowledge of the facts could be identified 100 percent correct in almost all examinations with the test of knowledge, that is, that no false-positive assignments were made.
The comparative questionnaire is not about possible factual knowledge, but the person to be examined is asked directly about the facts to be clarified, for example, whether he has committed the alleged act. Such a question may be in the reproach of sexual coercion, for example: “Have you ever kissed person X?” The questions on the allegation (usually there are three) are called questions of fact. They are related to (possibly four) comparative questions.
The methodological approach underlying the experimental setup is to compare a person’s responses to the tat-related questions with the same person’s responses to suggested comparison questions. The tat-related issues trigger a strong reaction on both the offender and the suspect. However, in the case of the wrongly suspect, the comparative questions trigger even stronger responses than the tat-related questions, while the offender cannot be distracted from the threat posed by the fact-related questions for him.
In order for the comparative questions to serve their purpose, they must be formulated so as to “occupy” the subject during the period of the investigation, thus “tampering” with their conscientious response. In order to achieve this, the comparative questions relate to the socially disapproved conduct of the person under investigation, in the same area of authority, which includes the deeds of which he is suspected.
Initially, a conversation is conducted with the subject, in which, in addition to a biographical anamnesis, the consumption of medicines, alcohol and drugs within the last 24 hours as well as the length of the bedtime during the previous night are inquired. Then, the questions to be examined are first discussed with the person to be examined, followed by the comparative questions. If both questions of fact and comparison are determined, the subject becomes familiar with the examination procedure and a trial run is carried out with him.