Several entities have begun to use the løgndetektor test performed by polygraph, to select candidates for some positions or to evaluate already-related personnel. Behind this decision is the belief that this is a good instrument to select or detect those who do not lie. It is therefore worth analyzing a procedure that is decisively affecting the work and personal life of many people. Such is the case of some of the prosecutors who were removed from the institution a few months ago, who complained about the offensive content of many of the questions they were subjected to with the polygraph, and even hinted that their departure had to do with the results of said test.
The polygraph, as its name implies (poly: multiples and graphos: strokes), records the skin reaction, systolic pressure, sweating and heart rate before different key questions, reactions that are compared to those obtained against control questions. This procedure dates back to 1920 and has been used frequently by government agencies in the United States, which have placed almost blind faith in its effectiveness.
However, it also has many detractors, which is why the U.S. Department of Energy created in 2000 a commission of scientists, belonging to the National Academy of Sciences, to independently judge the effectiveness of the polygraph. The commission was made up of professors from departments of psychology, biostatistics, neurology and medicine. Its function was to analyze the polygraph for the selection of personnel, a job that took about two years.
In Germany, on the other hand, the government appointed a professor from the University of Heidelberg. For a job similar to that of members of the Academy of Sciences and to give recommendations on the use of the polygraph in criminal cases.
Both reports have the merit of critically compiling the research on the subject and of being independent studies, since much of the information available comes from sellers of these devices or from entities that use them. To evaluate the use of the polygraph it is necessary to judge several aspects: its foundation, the procedure itself and the validity of the information obtained.
As for the basis, that is, in that the physiological responses tell us whether the person is lying or not, it is assumed that if the reactions to the questions are more intense than those against the neutral ones, the test is positive, it is say, the person is lying.
Conversely, if the reaction to key or critical questions does not reach the level of activation of control questions, the person is telling the truth. If both have a similar level, the result is inconclusive. In this regard, the Academy commission points out that although certain psychological states associated with telling lies (such as fear of being considered a liar) can produce physiological changes, these can also occur for other physical and psychological causes, among them, the undergo a test.
The control questions, which are repeated several times, include some about things that practically everyone has done but that people can deny (eg: have you ever taken something foreign?), And the reaction against these is compared to critics.
Additionally, it is assumed that in the case of lies, all physiological responses must be greater than when the truth is told. However, the physiological responses of the different channels are supposed to coincide in being high when there are lies and the reactions must be consistent in the different presentations of the questions.
Related to the above is the fact that the control questions are not standardized, that is, they are tailored to the person and are asked according to the experience of the polygraph operator. The control questions to establish a baseline or comparison are left to the expert’s intuition and the point is how he can be so intuitively ingenious to choose exactly the control questions that will serve as a cut-off point for the others.
Lie detectors may have weaknesses or inaccuracies, but so far they have proven to be effective in detecting lies in many people. Only a few people were really able to outsmart them. In conclusion, the lie detectors are still needed by institutions that need lie testing such as companies (in case of recruiting employees), police and military.