Detecting Deception

Polygraph Testing: A Critique

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One of the most commonly used methods for detecting deception is the polygraph test. This is a procedure that combines skillful questioning techniques with physical measurements in order to determine stress levels that would indicate the presence of deception. It is widely used and is reliable enough to be used in a court of law, if it is properly handled and interpreted by an expert in the field. New advances are taking this same base for technology and increasing its scope and range. However, there are issues of reliability that do come up, especially in regards to when a suspect uses counter measures to throw off the test. Thus, polygraphs are excellent tools for detecting deception, but should not be trusted entirely on their own. Instead, they should be used in a combined effort with other interviewing techniques to really be effective in detecting deception.


Using a to determine if an individual is in deed telling the truth is one of the most popularly used method for evaluating truthfulness. It has been around for decades now, every since it was first invented in the early 1920s. According to the readings, “the best known of the is the polygraph, which measures heart rate, skin conductance and respiration while a person is answering a number of questions” (Cooper et al., 304). The test itself was invented by a police officer, showing its roots in criminal justice. During the procedure, a suspect is asked a series of questions. Many of these questions are purposely simple in order to set a baseline for potential lies. Tings like what is your name and other simple questions are asked fist in order to allow the person administering the test to see how the person reacts to honest answers. These baseline questions are then compared to more loaded questions, where the suspect might actually try to lie.

A polygraph test is so accurate because it does not rely alone on inference to determine if someone is lying or telling the truth. In fact, it measures physical changes in an individual when asked to respond to certain questions. Yet, “the polygraph does not detect lies, it detects stress” (Cooper et al., 304). Things like heart rate, blood pressure, and breathing rate are all measured in order to detect any possible changes or reactions caused by being asked an uncomfortable question, where the suspect would then try to lie or avoid telling the truth. Thus, “the pretest interview is designed to ensure that subjects understand the questions and to induce a subject’s concern about being deceptive” (, 2014). The science of this is based on the reaction most individuals have to loaded questions and the stress they feel as they are about to lie. When an individual tries to lie, their stress rises. This is what is being detected by the polygraph. Examiners “today use computerized recording systems. Rate and depth of respiration are measured by pneumographs wrapped around a subject’s chest. Cardiovascular activity is assessed by a blood pressure cuff. Skin conductivity (called the galvanic skin or electrodermal response) is measured through electrodes attached to a subject’s fingertips” (American Psychological Association, 2014). All of these measurements can be used to thus infer the presence of deception.

Trained experts then interpret the readings to determine when, if any, lies are being told. These experts often used standardized tests ad questioning techniques during the course of a polygraph session. First, there is the , or the CQT. According to the research, this The CQT compares responses to ‘relevant’ questions (e.g., ‘Did you shoot your wife?’), with those of ‘control’ questions. The control questions are designed to control for the effect of the generally threatening nature of relevant questions. Control questions concern misdeeds that are similar to those being investigated, but refer to the subject’s past and are usually broad in scope; for example, ‘Have you ever betrayed anyone who trusted you?’” (American Psychological Association, 2014). Apparently, most people taking such a test would fear the control questions and thus have a reaction towards these control questions. This would help set a baseline for judging truthfulness. There is also a procedure known as the Guilty Knowledge Test (GKT). Here, the research claims that this procedure “involves developing a multiple-choice test with items concerning knowledge that only a guilty subject could have” (American Psychological Association, 2014). When the suspect knows guilty answers, he or she will have the reaction that signifies deception. This method for detecting deception has long been seen as reliable enough to stand in a court of law. Because of this, “ have become a popular cultural icon – from crime dramas to comedies to advertisements – the picture of a polygraph pen wildly gyrating on a moving chart is readily recognized symbol” (American Psychological Association, 2014). It is thus one of the most commonly thought of and used strategies for evaluating truthfulness and detecting deception.

However, there are a number of issues that arise with the use of polygraph tests as well. When polygraphs are administered by people who are not professionals, their reliability goes down dramatically in interpreting the physical signs of deception. Unfortunately, the “polygraph is a useful tool, but it has a focused use (e.g. criminal suspect investigations and national security) and can produce both false-positive and false-negative errors” (Cooper et al., 304). There are even situations where a polygraph can indicate deception where there is none at all. Essentially, “an honest person may be nervous when answering truthfully and a dishonest person may be non-anxious” (American Psychological Association, 2014). This would increase inefficiencies in the test and make it possibly dictate deception when there is none and vice versa. Additionally, there are a number of counter measures that can be used by the suspect in order to throw off the polygraph test as well. Suspects can purposely stress themselves out at simple questions to throw off the baseline analysis. Some even say that self-inducing pain during the process can throw off the stress detectors enough to have inconsistent results.

Still, the technology surrounding lie detector tests is rapidly evolving.

Voice stress analyzers “detect changes in the pitch and tension of the voice and there is no question that detecting change is an important aspect in evaluating truthfulness” (Cooper et al., 304). These tests can often be administered over much longer ranges, without the suspect re Cooper et al., ally knowing that he or she is being tested for truthfulness.


Overall, the polygraph is a very reliable tool for detecting truthfulness and deception; however, the results must be augmented with out deception detection techniques in order to really make for a strong case. Its methods are best used in conjunction with other interviewing techniques to be the most effective at detecting deception. Thus, “as with technology-based approaches, there is no single verbal or nonverbal channel that clearly communicates deception. Rather, research and clinical forensic experience suggest that it is the change in a particular channel and/or inconsistencies across channels that are particularly revealing” (Cooper et al., 305).


American Psychological Association. (2013). The truth about lie detectors. Research in Action. Web.

Cooper, Barry S., Herve, Hugues, & Yuille, John C. “Evaluating truthfulness: Detecting truths and lies in forensic contexts.