Polygraph

A polygraph, often mistakenly described as a lie detector, is a device used to measure physiological responses while an individual answers a structured series of questions. It records indicators such as blood pressure, pulse, respiration and electrodermal activity. The underlying assumption behind its use is that deceptive answers produce bodily reactions distinguishable from those produced by truthful answers. However, scientific consensus indicates that no specific physiological pattern is uniquely associated with lying. Because of this, polygraph testing is regarded by many scientific and professional bodies as a pseudoscientific practice.

Origins and Context

Polygraph examinations have been used in various countries for interrogating criminal suspects, assessing candidates for sensitive government or private-sector positions, and screening employees. In the United States, several law enforcement agencies and federal institutions employ polygraph examinations, sometimes referred to as psychophysiological detection of deception tests. Despite their widespread use in certain sectors, the reliability and validity of polygraphs have been repeatedly challenged.
Assessments by scientific organisations, including the American Psychological Association and the National Academy of Sciences, consistently highlight the limited accuracy of polygraph testing. Reports note that polygraphs can be defeated by relatively simple countermeasures and that results typically lack the precision required for high-stakes decision-making.

Testing Procedure

Polygraph examinations usually begin with a pre-test interview, during which the examiner gathers background information to construct diagnostic questions. The examiner then explains how the device purportedly detects deception and emphasises the importance of providing truthful answers. This is followed by a stim test in which the subject is asked to lie deliberately. The examiner then claims to identify the lie, reinforcing the perceived effectiveness of the device. Although intended to heighten anxiety in guilty individuals, this method can provoke equal or greater anxiety in innocent subjects.
In the main test, questions fall into three categories:

• Irrelevant questions: e.g., “Is your name John?”
• Control or diagnostic questions: designed to provoke a physiological reaction even in truthful subjects.
• Relevant questions: directly related to the investigation.

The Control Question Technique (CQT), commonly used in criminal investigations, assumes that truthful subjects react more strongly to control questions, whereas deceptive subjects react more strongly to relevant ones. Critics argue that CQT often resembles an interrogation, eliciting stress reactions in both innocent and guilty individuals and thereby compromising validity.
An alternative method, the Guilty Knowledge Test (GKT) or Concealed Information Test, is employed in Japan. This technique assesses whether the subject possesses crime-specific knowledge unlikely to be known by an innocent person. The test uses multiple-choice questions, each containing one correct answer related to the crime. A stronger physiological response to the correct option is interpreted as a sign of concealed knowledge. Supporters argue that this method reduces examiner bias and improves accuracy.

Scientific Evaluations and Limitations

Extensive scientific reviews highlight the polygraph’s limitations. The National Academy of Sciences’ 2003 report concluded that evidence supporting high accuracy is scientifically weak. The American Psychological Association likewise states that most psychologists find little empirical basis for detecting lies through physiological monitoring. Studies indicate that methods such as the relevant–irrelevant technique often produce false positives because innocent individuals may exhibit heightened reactions to crime-related questions.
A 2002 National Research Council assessment found that specific-incident polygraph tests can perform above chance levels in populations untrained in countermeasures but still fall far short of reliability standards required for forensic or employment decisions. The report cautioned against applying findings from controlled studies to real-world screening contexts, where accuracy is likely lower.
Courts have frequently criticised the scientific credibility of polygraphs. In United States v. Scheffer (1998), the Supreme Court held that polygraph evidence lacks consensus reliability and offers little more than subjective opinion. Subsequent rulings, such as decisions by the 11th Circuit Court of Appeals, reiterated that polygraphy is not generally accepted within the scientific community.
Scholarly critiques, including those by William Iacono, underscore several fundamental problems:

• CQT rests on assumptions that are naive and scientifically unsupported.
• Innocent individuals may be at particular risk of false detection.
• Countermeasures—such as intentionally enhancing reactions to control questions—can manipulate results.
• Polygraphs measure physiological arousal rather than deception.

Arousal can be triggered by numerous factors unrelated to dishonesty, including anxiety, fear, mental health conditions, metabolic states, substance use, and withdrawal symptoms. Consequently, the device cannot distinguish between the emotional stress of lying and the stress caused by unrelated factors.
Efforts to augment polygraph accuracy through additional technologies, such as microexpression analysis in the Silent Talker system, have similarly failed to produce reliable lie detection outcomes.

Government Reviews and Public Policy

A 1983 review by the U.S. Congress Office of Technology Assessment and subsequent analyses emphasised the lack of scientific grounding for polygraph accuracy. The National Academy of Sciences’ 2003 report found that many of the studies used by polygraph advocates suffered from methodological flaws, and that real-world accuracy is almost certainly lower than experimental findings suggest.
Despite these critiques, polygraph testing continues to be used in certain investigative and employment settings, primarily as a psychological tool to elicit confessions or encourage compliance rather than as a scientifically validated method for detecting deception.