More About Polygraph

What Does a Typical polygraph Examination entail?

There are typically three phases: a pre-test phase, and in-test phase, and a post-test phase, which includes the scrutiny of the recorded test data and analysis. This process can last for at least two hours, but sometimes longer. In the in-test phase, normally three charts will be recorded.

Pre-test ~ is where the polygraph examiner will complete all the formal documents and discuss the procedure, and the instrument, with the examinee. Specifically the examiner will carefully review the questions to be asked in relation to the specific issues being addressed. A statement will then be taken, following a summary of the case facts. Sometimes the sensors are attached so as to perform a "stimulation test," which is a demonstration of the instrument's accuracy in detecting deception.

In-test ~ is when the actual charts are recorded. This starts with the examinee being attached to the polygraph, and then asked the previously discussed questions in a 'yes' 'no' fashion. The data is collected by the sensors and recorded electronically. There are several questioning techniques commonly used, however, the most well used format is the Control Question Test (CQT). The CQT is a comparison of responses to three 'relevant' questions (e.g. "Did you distribute child pornography?"), with 'Control' questions (e.g. Did you ever take part in an unnatural sex act?). These control questions are designed to control for the effect of the specifically disconcerting nature of the relevant questions. The control questions are widely perpetrated misdemeanours, but are similar to those at issue, and refer to historical actions on the part of the examinee.

The person who is truthful will orient more towards the control questions than the relevant questions because the control questions were developed to instil concern about past truthfulness, while the relevant questions are less threatening because they know they have not committed them. If the chart shows a greater pattern of responding to relevant questions than to the control questions, then the examinee will be deemed "deceptive." If there is no difference between the relevant and control questions then the exam is considered to be "inconclusive."

Post-Test is where the polygraph examiner will analyze the data on the chart recordings and give an opinion as the truthfulness or honesty of the examinee. An opportunity to explain the physiological reactions in relation to the questions will normally be given to the examinee.

The Detection of Concealed Information

The Concealed Information Test (CIT), or sometimes referred to as the Guilty Knowledge Test, uses a set of multiple-choice questions which refer to crime-specific details of the investigation in hand. For example in the case of a homicide, "The murder scene was.....:

The assumptions being that those suspects who possess "guilty knowledge" will recognise the crime-relevant information and react more strongly to relevant items than to irrelevant items; and those with no "guilty knowledge" will have no differential reactions to either relevant or irrelevant items. The advantage, therefore, is that for innocents there is a very low risk of being misclassified as "guilty" Research has found that the accuracy is in the region of a 95% hit rate, and that most studies reported no false positive results, i.e. misclassifying the innocent as guilty.

How Accurate is the Polygraph?

The scientific data concerning the validity of the polygraph can be summarised as follows: High quality scientific research from the laboratory-based and those studies conducted in real cases, so-called field research, have concluded that the CQT is a highly accurate discriminator of truth tellers from deceivers. The research results converge on an accuracy estimate that exceeds 90% in laboratory studies and 98% in field studies. However, users are cautioned that false positive results do occur, and the instances of such events is not negligible. According to research on this matter, there is a 25% chance that innocents will be wrongly classified as being deceptive (i.e 75% will be correctly deemed as being innocent). Every possible effort will be made to reduce the occurrence of such results. Due to the fact that there is no machine which can detect when a person is deceptive with a 100% accuracy, the polygraph results are used in conjuction with other collateral sources of information. Thus there must be indications from several observations before any final opinion is reported.

What about Countermeasures?

A countermeasure can be described as anything that an examinee might do in order to distort or defeat a polygraph test. Detailed reviews of the scientific literature on countermeasures have concluded that there is no credible evidence that drugs or other measures designed to affect the general state of the examinee are effective against the CQT. However, studies have indicated that training in specific point countermeasures that increase responding to control questions is effective in producing an increase in inconclusive and false negative outcomes. Nevertheless, the highly trained polygraph examiner and recent developments in combating countermeasures, such as an activity monitor, can usually detect such behaviours.

Advice for Individuals Intending a Polygraph Examination.

You will require a valid photograph ID, such as a Passport or Driver's Licence, and a written statement of the incident under investigation (if required). You should not be overtired, and be free from any intoxicating substances. Women who are pregnant, individuals with high blood pressure or cardiovascular diseases, muscular disorders, respiratory disease, diagnosed with a mental illness such as bi-polar disorder or clinical depression, and unaided hearing impairments will not be examined unless written permission is received from their treating physician. In addition, any person we determine to be physically or mentally unfit for examination will not be tested. The examinee should not be questioned about any issues on the actual day of the test, i.e. prior to meeting the examiner, as this may adversely affect the results.

How to Schedule a Polygraph Examination

You can schedule a polygraph examination by calling CFN on Freephone 0800 520 0235, or, by using our secure contact form, and we will get back to you as soon as possible to assist your investigation needs.