Properly administered, the polygraph technique is a non-accusatory diagnostic procedure that allows an examiner to collect physiological data to infer whether or not a subject is telling the truth to relevant questions (see August web tip). Accusatory interrogation has no place in a properly conduced polygraph examination (Reid and Inbau, Truth and Deception the Polygraph "Lie-detector" Technique, Williams and Wilkins, 1977). Unfortunately, the private environment and intimate relationship an examiner forms with a subject during a polygraph examination creates an ideal breeding ground for a confession. This factor is significant enough that some state supreme courts have ruled that taking a polygraph examination is so inherently coercive that any confession made during the course of a polygraph examination should be suppressed. It should be understood that a confession obtained during an interrogation following a polygraph examination is accepted in all states.
Since the polygraph is not a lie-detector, its usefulness during an investigation is entirely dependent on the competency of the examiner. A competent examiner will be accurate in determining truth or deception approximately 90% of the time (based strictly on chart analysis). This figure will increase if the examiner incorporates other means of detecting deception such as behavior symptom analysis. The competent examiner will be unable to render a definite opinion of truth or deception in about 10% of subjects examined. An examiner who boasts of an accuracy rate above 95% and an inconclusive rate less than 5% should be avoided.
Training in the polygraph technique can range from two to six months of instruction. The best training programs include not only the basic class-room instruction, but an internship period as well. During this internship the student's charts and procedures are carefully scrutinized to develop clinical skills. Following this training and obtaining a license, if required, competent examiners will join a professional organization such as the American Polygraph Association or the Association of Police Polygraphists.
An important part of an examiner's training is to identify those subjects who are at risk for producing erroneous results. The ideal subject is one of average, or above average intelligence, who is not mentally impaired and is in reasonably good medical health. It is also important that the subject's emotional state is relatively stable during the examination. A leading cause for false positive results (reporting a truthful subject as deceptive) is anger within the subject. This anger may be caused by prior interrogation or an accusatory pre-test interview. Inadequate development or selection of control questions is another cause for false positive results.
False negative results (reporting a deceptive subject as innocent) may be the result of improper question formulation in which relevant questions are phrased in such a way that they do not present a significant threat to the guilty person. Subjects with a lower intelligence may also increase the risk of a false negative result. In some cases, a guilty subject may engage in countermeasures that the examiner fails to recognize during chart analysis. Identifying countermeasures is a critical part of a competent examiner's training. In our office almost 25% of guilty suspects are identified primarily because of their use of countermeasures. Innocent subjects allow their body to respond normally during a polygraph examination. It is the guilty subject who will consciously try to manipulate the polygraph recordings. In this regard, agencies should be very cautious when using an examiner who relies exclusively on computer analyzed charts. None of the software developed for this purpose is capable of identifying specific subject countermeasures.
Another aspect of a competent examiner's training is to identify unsuitable subjects. Generally speaking, children under the age of 14 are not suitable for the polygraph technique. Subjects with significant mental disorders, such as diminished mental capacity or symptoms of detachment from reality are often not suitable for the technique. The subject's mental state is also an important consideration. Fatigue, intoxication, anguish and trauma may each render a subject unsuitable for the polygraph technique.
Without a doubt, however, the greatest risk for erroneous polygraph opinions is outside pressure. Agencies place tremendous pressure on polygraph examiners to obtain findings consistent with predetermined expectations. There is pressure to form an opinion in every case and, when a subject produces deceptive polygraph results, to obtain a confession from that subject. For these reasons the position of a polygraph examiner should be somewhat autonomous from other agency functions. The personality of the examiner should be such that he or she is an analytic thinker and possess a great deal of self-confidence with little interest in pleasing others or advancing in rank through politics.
With this background, the following are recommendations for the proper use of the polygraph technique during an investigation:
Only use a well-trained, competent examiner;
For legal reasons, do not use the polygraph as a ruse to get a guilty suspect into a controlled environment merely to conduct an interrogation;
Avoid engaging in accusatory interrogation if the suspect may be willing to take a polygraph examination;
Accept the examiner's opinion that a particular subject is unsuitable;
Do not place pressure on an examiner for a definitive opinion -10% are inconclusive;
Do not rely on an examiner to solve your cases with a confession. The technique should serve as a diagnostic investigative aid to establish a person's truthfulness.