Legal Limits: When Lie Detector Tests Are Allowed And When They Aren’t

Lie detector test admissibility remains a sharply divisive issue. 

According to proponents, polygraph findings should be allowed in judicial proceedings as supportive evidence. Champions of lie detector tests assess that the procedure can be remarkably effective at sniffing out liars if professionally administered. 

However, polygraph opponents think entirely otherwise. Critics hold that lie detector test reports should be inadmissible since the practice lacks overwhelming backing within its scientific community. 

So, when should polygraph findings be legally acceptable and when shouldn’t they? 

Read below as we put that question in a better perspective. 

When Polygraph Findings Aren’t Allowed?

1. Evidence in Criminal Proceedings

Polygraph is synonymous with law enforcement. While the practice has since found significance in other sectors, such as relationship therapy and immigration vetting, criminal investigations still claim a significant portion of lie detector tests. 

Surprisingly, polygraph findings are generally inadmissible in criminal proceedings. 

A litigant may request a lie detector test. However, most courts will disallow the findings for lack of solid scientific backing.

2. Evidence in Federal Trials 

The United States federal government is perhaps the most outspoken opponent of lie detector tests. 

So, it’s unsurprising that polygraph findings are largely inadmissible in federal proceedings. 

We should point out that federal courts don’t impose sweeping bans on lie detector tests. However, recent rulings - such as the U.S. v. Scheffer - have consistently ruled against the inclusion of polygraph evidence. 

3. Proof of Standard Violation

To conduct legally defensible lie detector tests, examiners must comply with certain industry standards. 

First, examinees must submit their wilful, informed consent in writing. Examiners cannot coerce subjects or lure them with incentives. 

Besides, polygraph exams should unfold in three critical stages as follows;

Pre-test

Pre-test involves collecting an examinee’s physiological baselines. 

Using baseline data as a benchmark, examiners can gauge the variance in response to in-test questions and infer deception more accurately. 

Other key events at the pre-test phase include reconfirming consent, calibrating the polygraph machine through acquaintance testing, and explaining how the procedure goes.

In-test

During the in-test phase, examiners pose a series of Relevant and Control questions to the examinee. Each response triggers changes in heart rate, breathing, and skin conductivity...all recorded by the polygraph machine in real-time. 

Industry standards mandate examiners to ask questions in a neutral, non-accusatory tone. 

In-test queries should also be straightforward. There’s no room for ambiguity. 

Besides, the questions must attract a flat ‘Yes’ or ‘No’ response. 

Post-test

The post-test phase involves examiners analyzing an examinee’s responses to infer deception or honesty. 

A stronger magnitude of response to Relevant than Control questions suggests deception, while the converse indicates truthfulness. 

Note: All three phases occur in a single polygraph test, which lasts an average of 1.5 – 2.5 hours. 

Why Are Polygraph Tests Legally Restricted?

1. Generally Unreliable

Polygraph exams measure changes in certain physiological reactions associated with deception, making them more reliable than competitive techniques like Computer Voice Stress Analyzer (CVSA). 

However, many courts have ruled that lie detector tests fall short of the Daubert standard for evidence admissibility. 

To fulfill the Daubert standard, a scientific technique or theory must have;

• Been tested and tried

• Been peer-reviewed

• Zero or minimum error rate

• Known control standards

• Garnered significant acceptance within its immediate scientific community.

2. Potential for Jury Bias

Many assess that admitting polygraph exams can lead to jury bias, causing overreliance on lie detector tests at the expense of more credible scientific evidence. 

Further, critics hold that even professionally administered lie detector tests wouldn’t assist the trier of fact spelled out under Rule 702. 

3. Potential Use of Countermeasures

Countermeasures are deliberate attempts by examinees to beat a polygraph test. They can be;

• Physical, such as suppressing breathing

• Pharmacological, such as taking antidepressants

• Mental, such as attempting to block certain memories

Although countermeasures are commonly deployed by guilty subjects, innocent examinees may also resort to these tactics to prove their innocence. 

Note that examinees are trained on countermeasure detection. While that technically renders these tactics ineffective, their potential use presents a valid reason for disowning polygraph findings.

When Might Polygraph Tests Be Allowed?

1. Non-criminal Proceedings

While polygraph admissibility remains a thorny issue in criminal proceedings, the findings may be allowed in other scenarios, like;

• Law enforcement pre-employment screening (LEPET)

• Pre-trial negotiations, such as plea bargaining

• Sex offender parole compliance monitoring

• Screening for banned substances in sports

• Relationship counseling

• Addiction therapy

• Immigration testing

• Prequalifying government contractors

• Intelligence gathering by national security agencies like the FBI

2. As Supportive Evidence

Polygraph findings may provide supportive evidence, especially where an individual’s credibility is under intense scrutiny.

Lie detector tests are commonly suggested where there’s compelling circumstantial evidence to go on. Even so, the reports shouldn’t be applied probatively. 

3. Mutual Agreement

For lie detector tests to be legally binding, both parties must consent to using the findings. 

In formal judicial processes, the said agreement would involve the prosecution and defense counsel. 

The Bottom Line

Polygraph’s admissibility varies by jurisdiction. 

In most countries and states that allow lie detector tests, the findings are typically used in civil rather than criminal proceedings. And even then, admissibility usually rests upon the presiding judge or jury. 

To conduct a legally defensible lie detector test, examiners must observe all industry standards. Those include obtaining the examinee’s consent in writing, asking questions in a non-accusatory tone, and interpreting the findings objectively. 

More importantly, polygraph findings must strictly serve as secondary evidence. That means examinees should only be subjected to lie detector tests to corroborate or impeach reasonable doubts, suspicion, or circumstantial evidence.