Polygraph Test Admissibility
Polygraph Test Admissibility: Overview
A polygraph test (commonly known as a lie detector test) measures physiological responses such as heart rate, blood pressure, respiration, and skin conductivity while a person answers questions. The theory is that deceptive answers will produce physiological responses that differ from truthful ones.
Admissibility refers to whether polygraph evidence can be used in court proceedings. Courts are generally cautious because:
The scientific reliability of polygraphs has been questioned.
Results can be influenced by various factors (nervousness, examiner bias, etc.).
The test is not 100% accurate.
As a result, many jurisdictions either exclude polygraph results as evidence or allow them only under strict conditions (e.g., both parties consent).
Key Cases on Polygraph Admissibility
1. Frye v. United States (1923)
Jurisdiction: U.S. Federal Court
Summary: This landmark case established the "general acceptance" test for scientific evidence admissibility.
Facts: The defendant wanted to admit the results of a systolic blood pressure deception test (an early form of polygraph) to prove innocence.
Holding: The court ruled that scientific evidence is admissible only if the method is "generally accepted" by the relevant scientific community.
Impact on Polygraph: Since polygraph technology was not generally accepted as reliable by the scientific community at that time, the court excluded the evidence.
Significance: Frye set a high bar for polygraph admissibility; polygraphs have often failed this standard.
2. United States v. Scheffer (1998)
Jurisdiction: U.S. Supreme Court
Summary: The Court ruled on whether a military trial could exclude polygraph results.
Facts: The defendant wanted to introduce polygraph evidence to support his innocence during a court-martial.
Holding: The Court upheld a military rule that categorically excludes polygraph evidence, reasoning that the military has broad discretion in its procedures, and there is no constitutional right to introduce polygraph results.
Impact: The decision affirmed that polygraph evidence is not inherently admissible and that courts have broad discretion to exclude it.
Key point: The Court did not comment on polygraph reliability but emphasized the government's interest in excluding unreliable evidence.
3. People v. Leahy (1981)
Jurisdiction: California Supreme Court
Summary: This case addressed the admissibility of polygraph results under California law.
Facts: The defendant sought to admit polygraph evidence to prove innocence.
Holding: The court held polygraph evidence inadmissible due to its questionable scientific validity.
Impact: This case reinforced the idea that polygraph tests are generally inadmissible as evidence in California courts.
Additional note: The court allowed that polygraph evidence might be admitted if both parties consent and under strict evidentiary controls.
4. State v. Scheibe (1990)
Jurisdiction: Oregon Supreme Court
Summary: This case examined whether polygraph evidence could be admitted during a criminal trial.
Facts: The defendant wished to introduce polygraph results to challenge prosecution evidence.
Holding: The court ruled polygraph evidence inadmissible due to a lack of scientific consensus about its reliability.
Impact: The ruling reaffirmed the strict scrutiny courts apply before admitting polygraph results.
Additional point: The court emphasized the risk of prejudice and confusion outweighs the probative value of the test.
5. Commonwealth v. Caserta (1979)
Jurisdiction: Massachusetts Supreme Judicial Court
Summary: This case dealt with polygraph evidence admissibility.
Facts: The defendant attempted to introduce polygraph results to prove innocence.
Holding: The court rejected polygraph evidence, citing concerns about accuracy and potential prejudice.
Impact: The decision underscored skepticism toward polygraph tests in Massachusetts courts.
Additional note: The court acknowledged the test's potential use in investigations but not in trials.
6. United States v. Post (1988)
Jurisdiction: U.S. District Court, District of Utah
Summary: This case is notable for allowing polygraph evidence under certain conditions.
Facts: The defendant agreed to a polygraph exam and wanted to introduce the results.
Holding: The court admitted polygraph results because both parties consented and the examiner’s methodology was thoroughly scrutinized.
Impact: Demonstrated that consent and stringent procedural safeguards can lead to polygraph admissibility in some courts.
Key takeaway: Consent of both parties and expert testimony about test reliability are crucial.
Summary and Practical Implications
General Rule: Polygraph evidence is usually inadmissible in courts due to questions about reliability.
Exceptions: Polygraph results may be admitted if:
Both parties agree (stipulation).
The test administration and methodology meet strict standards.
The court finds it relevant and not unduly prejudicial.
Policy Considerations: Courts worry polygraphs can mislead juries or cause unfair prejudice.
Use in Investigation: Polygraphs are often used by law enforcement and employers as investigative tools, but this does not mean their results are automatically admissible in court.
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