The legal system generally excludes the results of polygraph examinations from use as evidence. These devices, often referred to as lie detectors, measure physiological responses such as heart rate, blood pressure, respiration, and skin conductivity while an individual answers questions. The premise is that deceptive answers will trigger measurable changes in these physiological indicators. A common scenario involves law enforcement seeking a confession or using the results to guide an investigation; however, presenting the outcome of the assessment directly in court is typically prohibited.
The inadmissibility stems from concerns about reliability and validity. Scientific studies have consistently shown that polygraph tests are susceptible to error, producing both false positives (identifying truthful individuals as deceptive) and false negatives (failing to identify deceptive individuals). Furthermore, an individual’s ability to manipulate physiological responses, whether consciously or unconsciously, further undermines the accuracy of the examination. Allowing these results as evidence could unfairly prejudice a jury, leading to unjust outcomes. The historical context reveals a gradual erosion of judicial confidence in the technology as scientific understanding of its limitations deepened.
