While polygraph tests are grounded in physiological science, their reliability and admissibility remain debated within the broader scientific and legal communities.
Lie detector tests measure deviations from an individual’s physiological baselines, focusing on core biological functions like breathing, heart rate, and skin conductance. Multiple studies have demonstrated that lying can impact the autonomic nervous system (ANS), which regulates these vital functions.
Since the polygraph is based on science, every lie detector test must satisfy certain forensic standards to be deemed credible. Here’s a look at some of those protocols.
1. Using Evidence-Based Validation Techniques
One of the best practices in forensics is that every investigation must utilize evidence-based validation methods. Professional examiners should follow APA-validated methods such as the Zone Comparison Test (ZCT), Modified General Question Test (MGQT), or other standardized formats supported by empirical studies.
To conduct a credible polygraph test, insist on an examiner who uses industry-acknowledged techniques. The American Polygraph Association (APA) has published standards for evidence-based polygraph validation techniques. If an examiner uses a methodology that’s unrecognized by the APA, they must explain that in writing.
2. Systematic Evidence Gathering
Forensic investigations follow clearly defined procedures, typically commencing from preparations and culminating in report writing. The same should apply to lie detector tests.
Polygraph exams occur at three critical stages. Here’s what each phase entails;
Pre-test Phase
The pre-test phase takes place immediately before the polygraph examination, as part of the same scheduled session. It involves:
- Establishing rapport and explaining the purpose of the exam.
- Informing the examinee about the test process and its implications.
- Obtaining written informed consent from the examinee.
- Preparing and reviewing the list of polygraph questions.
- Conducting baseline physiological readings to establish the examinee’s normal response patterns.
In-test Phase
- Examiner attaches polygraph instrument sensors to the examinee’s body
- Examiner asks the list of questions prepared in the pre-test phase
- Polygraph instrument records each reply in real-time
Post-test Phase
- Examiner invites the examinee to explain some of their responses
- Examiner prepares the final polygraph report
- Content of the report disclosed to the client
3. Clarity and Unambiguity
Like forensic investigations, polygraph questions must be straight and closed-ended.
The in-test queries should attract a straightforward ‘Yes’ or ‘No’ reply. Narrative replies are prohibited.
Besides, the examinee must understand the question as anyone else would. There’s no room for ambiguity. This minimizes the time and emotional stress the examinee requires to answer a polygraph question.
4. Strict Investigation Timelines
Forensic investigations don’t last forever. There comes a time when detectives must wrap up a case and present their findings. When it comes to lie detector tests, the ideal length for polygraph investigations is 1.5 – 2.5 hours. That duration encompasses all three critical phases.
5. Doctrine of Innocence Until Proven Guilty
Even if a suspect was captured on CCTV surveillance committing a crime, they’re presumed innocent until proven otherwise. It’s not a detective’s role to establish guilt.
The same goes for polygraph tests.
Examiners shouldn’t treat examinees as guilty even if all available evidence incriminates them. That means polygraphers must remain objective throughout the testing, avoiding posing questions in an accusatory or speculative tone.
6. Rule of Evidence Admissibility
To be admitted in legal proceedings, polygraph tests must satisfy the rule of evidence of admissibility as highlighted in the Daubert standard.
Note that most lie detector tests, except for single-issue exams, fall short of the Daubert standard. As such, the findings can only be used as supportive rather than probative evidence.
7. Evidence Cannot Be Used In Isolation
Polygraph findings shouldn’t be the fundamental basis for convicting or exonerating a suspect.
As mentioned, the results must be used alongside other evidence.
The fact that most lie detector tests don’t meet the Daubert standard underscores the significance of using the findings strictly to corroborate or impeach primary evidence.
8. Guidelines on Scoring
At the end of a polygraph exam, an examiner must analyze individual responses to every question and give their professional scoring.
Polygraphers interpret lie detector tests by comparing the pattern of response to relevant and control questions. Examinees who respond strongly to relevant questions are likely to be guilty, while a stronger response to control questions than to relevant questions indicates innocence.
9. Ethical Considerations
All forensic investigations must uphold certain ethical considerations for the findings to be deemed valid.
In polygraphs, examiners should seek a written consent from examinees before subjecting them to lie detector tests. Using force or coercion is prohibited.
Other ethical considerations include upholding the examinee’s right to privacy and treating them with dignity.
10. Collaborative Approach
Forensic detectives don’t work in isolation. Instead, they partner with several other professionals whose expertise can be invaluable in cracking a case.
Polygraphers don’t work alone either. They collaborate with different industry stakeholders, depending on the type of lie detector test undertaken.
For instance, law enforcement examiners work closely with criminal detectives and prosecutors. Private examiners who work in therapeutic settings would maintain close networks with relationship counselors and addiction therapists.
Meeting Forensic Thresholds Through Professional Polygraph Tests
Polygraph results can influence critical decisions in investigations, employment, or legal negotiations—highlighting the need for professionally conducted exams.
Since there’s a lot at stake, it’s best to have all polygraphs administered by a qualified examiner who understands the best practices in forensic investigations. This ensures the findings are not only accurate but also legally defensible.
