Over a century has passed since the polygraph was first developed. This test measures physiological responses such as blood pressure, pulse, and breathing to determine whether someone is lying or telling the truth. Is polygraph evidence admissible in court if it’s accurate and reliable?
How accurate are polygraph tests?
Early claims of polygraph accuracy were inflated, with some exponents boasting 95% reliability. However, research has indicated a significantly lower accuracy rate. Factors impacting accuracy include:
- Experience and skill of the examiner – examiner errors significantly influence results
- Subject countermeasures – subjects attempt to manipulate results through techniques that alter responses
- Subject traits – accuracy varies based on subject age, gender, health status, medication use, and other traits
- Examiner bias – an examiner’s preconceived ideas about the subject impact interpretation
- Research design flaws – many studies have not followed scientific protocols
- Base rate issue – with a low base rate of deception, high accuracy is difficult to achieve
Upon detecting deception, polygraph analytics were estimated to be 89% accurate, and 73% accurate when determining non-deception. Since the factors above are generally known, real-world accuracy may be lower. Many experts believe 50-60% accuracy under field conditions is more realistic. Due to these limitations, polygraph evidence is not universally admissible in court. Evaluating its credibility involves weighing the benefits against the risks of unfair prejudice, including the “aura of infallibility” the test often evokes.
Legal implications of lie detector tests
The 1921 Frye v. United States case established an important precedence – for expert testimony and scientific evidence to be admissible, it must have “gained general acceptance in the particular field in which it belongs”. This standard was applied to polygraph testing, which resulted in it being inadmissible for over 50 years. It wasn’t until the 1975 US v. Ridling case that a federal court first recognized polygraph results as admissible evidence. Today, polygraph admissibility varies between states and situations. A few states allow polygraph evidence, while others prohibit it outright. There are no definitive rulings from the Supreme Court regarding admissibility at the federal level.
Where polygraph results are admissible, a few key considerations apply:
- Both parties must jointly stipulate the test procedures and scope of admissibility before it is administered.
- Results are often only allowed as supplementary evidence, not as standalone proof due to limited reliability.
- The judge informs the jury that polygraph results do not constitute definitive proof. The jury weighs up validity and relevance.
- Experts called to debate validity, with an examination of the examiner’s qualifications, testing procedures, and other factors.
While lie detector test locations across USA has made advances, concerns remain about accuracy and misplaced perceptions. But used judiciously under strict protocols, lie detector tests provide useful supporting evidence – though the legal system seems unlikely to rely on them more heavily anytime soon.
