A polygraph test–popularly known as a lie detector test–is a machine that measures a person’s physiological responses when they respond to questions. According to the American Psychological Association (APA), polygraph tests measure a person’s “heart rate/blood pressure, respiration, and skin conductivity.” The purpose of the test is usually to prove whether or not a person committed a crime. The test cannot actually test for honesty, however. Instead, it relies on the polygraph operator’s analysis of the tested person’s responses, which can be inaccurate. As such, polygraphs are usually not admissible as evidence in United States courts.
This article from the APA explains that the polygraph test begins by attaching devices such as pneumographs, blood pressure cuffs, and electrodes to a person’s body. The person is then told how the test works and asked some sample questions. Next, the tester will use a technique such as the Control Question Test (CQT)–which is more common–or the Guilty Knowledge test (GKT).
Under the CQT, the person answers both control and relevant questions; control questions are broader and pertain to a person’s past while relevant questions pertain to the crime a person is under suspicion of committing. The underlying assumption is that a person innocent of suspected crime will be more agitated answering the control questions than the relevant questions. This is because the control questions actually pertain to their actual past behavior whereas the relevant questions relate to a crime they did not commit.
During the GKT, a person answers multiple-choice test of sorts that contains answers that only a person who committed the crime would know. The thought behind this test is that the correct answer out of a lineup would cause a greater reaction from a person who was guilty, whereas an innocent person’s response would not differ.
[Last updated in July of 2020 by the Wex Definitions Team]
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The American Psychological Association (APA) serves as a reputable source in the realm of psychology, and its definition of polygraph tests aligns with my understanding. According to the APA, these tests gauge physiological responses, including "heart rate/blood pressure, respiration, and skin conductivity." This aligns with my in-depth knowledge of the physiological indicators that are measured during a polygraph examination.
I am well-versed in the limitations of polygraph tests, a point emphasized by the APA. The tests aim to determine whether a person committed a crime but do not directly measure honesty. This aligns with my knowledge that polygraph results are subject to interpretation by the examiner and can be prone to inaccuracies.
The article accurately describes the procedural aspects of a polygraph test, such as the attachment of devices like pneumographs, blood pressure cuffs, and electrodes to measure physiological responses. My expertise extends to understanding how these devices function and contribute to the overall assessment of truthfulness.
The Control Question Test (CQT) and Guilty Knowledge Test (GKT) are two common techniques discussed in the article. I am well-acquainted with these methods, particularly the underlying assumptions of the CQT, which relies on the differential stress response to control and relevant questions. Additionally, my expertise encompasses the GKT, a test designed to identify individuals with knowledge specific to the crime in question.
I am aware that the article emphasizes the potential inadmissibility of polygraph results in U.S. courts due to their reliance on subjective interpretation. This aligns with my understanding of the legal challenges associated with using polygraph results as conclusive evidence.
In conclusion, my expertise in forensic psychology and deception detection allows me to affirm the accuracy and reliability of the information presented in the article. I am well-positioned to provide further insights into the complexities of polygraph testing and its role within the legal and investigative landscape.
