The polygraph is often misunderstood as a simple lie detector. In forensic practice, its value lies in structured questioning, professional interpretation, and its ability to support disclosure in appropriate legal, clinical, and investigative contexts.
Introduction: Why Grubin’s Article Matters
In 2010, Professor Don Grubin published “The Polygraph and Forensic Psychiatry” in the Journal of the American Academy of Psychiatry and the Law. The article remains one of the most important contributions to the professional discussion of polygraph testing in clinical and forensic settings.
Grubin’s central argument is straightforward: the polygraph does not detect lies. It records physiological responses — changes in electrodermal activity, cardiovascular function, and respiration — while an examinee processes carefully structured questions. The value of the procedure lies not in any magical ability to identify deception, but in the structured methodology, the quality of the questions asked, and the expertise of the professional interpreting the results.
This article is important because it moves the conversation away from simplistic ideas of “lie detection” and towards a more responsible, evidence-led understanding of what polygraph testing can and cannot achieve. For anyone involved in forensic psychiatry, forensic psychology, risk assessment, or credibility assessment, the principles Grubin describes remain directly relevant.
Polygraph Testing Is Not Simply About “Passing” or “Failing”
One of Grubin’s most important observations is that the test result itself — whether the outcome is recorded as “deception indicated,” “no deception indicated,” or “inconclusive” — is only one part of the process. In many clinical and forensic contexts, disclosure is equally significant.
Grubin describes how the structured pre-test interview, the in-test procedure, and the post-test review can each contribute to the emergence of relevant information. For reasons that are not yet fully understood, the polygraph process appears to facilitate disclosure — encouraging examinees to provide information they might otherwise withhold. This does not mean the polygraph guarantees truth. It means the structured process, delivered by a trained professional, can create conditions in which relevant information is more likely to be discussed openly.
This is a critical distinction. The polygraph examination is not a pass-or-fail test in the way a blood test might be. It is a structured forensic procedure in which the process of questioning, the physiological data recorded, and the information disclosed all contribute to the overall assessment.
The Importance of Forensic Expertise
The polygraph instrument records physiological data. It does not interpret that data. Professional interpretation is essential — and this requires training, experience, and a sound understanding of psychophysiology, question design, and the specific context in which the examination takes place.
Grubin makes clear that the quality of a polygraph examination depends on the competence of the examiner: the clarity of the questions, the structure of the test format, the ethical conduct of the procedure, and the care taken in reporting the results. Without this professional framework, the data recorded by the instrument has limited value.
At the Centre for Forensic Neuroscience, Dr Keith Ashcroft applies these principles to every examination. Each case is assessed for suitability, questions are carefully formulated, and results are interpreted within the context of the available evidence, the specific questions asked, and the wider circumstances of the matter. This approach reflects Grubin’s emphasis on forensic expertise as the foundation of responsible polygraph practice.
Disclosure, Risk, and Behavioural Assessment
Grubin’s article highlights the value of polygraph testing in settings where disclosure is particularly important. In appropriate circumstances, polygraph examinations may support the assessment process in contexts such as:
- Sexual history disclosure in therapeutic or supervisory settings
- Workplace misconduct investigations
- Breach of supervision or behavioural conditions
- Relationship and trust-related disclosures
- Safeguarding-sensitive concerns
- Specific-issue investigations where clarification of a defined matter is required
In each of these contexts, the polygraph examination can support — but does not replace — legal, clinical, investigative, or organisational decision-making. The results must always be considered as one component of a wider assessment, not as a standalone finding.
Why Question Formulation Is Critical
Grubin emphasises that the polygraph records physiological responses to specific questions. If those questions are vague, ambiguous, or emotionally loaded, the data produced may be difficult to interpret meaningfully. Clear, behaviour-specific, yes/no questions are essential to a professionally defensible examination.
Consider the following comparison:
Poor example: “Have you ever behaved dishonestly?”
Better example: “On 12 March 2026, did you remove company documents from the restricted file without authorisation?”
The first question is too broad. Almost anyone could interpret it in multiple ways, and the physiological response it produces may reflect confusion, uncertainty, or general anxiety rather than anything relevant to the specific issue under investigation. The second question is anchored to a defined event, a specific date, and a clear behaviour. This makes it possible to interpret the physiological data within a meaningful forensic context.
Careful question formulation is not an optional refinement — it is fundamental to the validity and usefulness of the entire examination.
Polygraph Results Should Never Be Treated in Isolation
Grubin is clear that polygraph findings must be interpreted alongside other available information. A polygraph result, whether indicative of deception or not, should be considered in the context of:
- Documentary evidence and records
- Witness accounts and third-party information
- Digital evidence and communications
- Behavioural history and risk factors
- Clinical or psychological assessments
- Any other relevant material available to the instructing party
Transparent reporting is essential. A professionally prepared polygraph report should clearly state the methodology used, the questions asked, the physiological data recorded, the interpretation reached, and the limitations of that interpretation. This approach ensures that instructing solicitors, clinical teams, employers, and other decision-makers can weigh the polygraph findings appropriately within the wider body of evidence.
Where Polygraph Examinations May Assist
Drawing on the principles described by Grubin, polygraph examinations may be appropriate in a range of forensic, legal, corporate, and private contexts, including:
- Solicitor-led instructions in civil or family proceedings
- Corporate investigations into misconduct, policy breaches, or regulatory concerns
- Theft, fraud, sabotage, or insider-risk matters
- Relationship and family credibility issues
- Sexual behaviour disclosure in therapeutic or supervisory contexts
- Safeguarding-sensitive concerns
- Confidential private client matters
In every case, suitability must be assessed before proceeding. Not all matters are appropriate for polygraph examination, and the Centre for Forensic Neuroscience reviews each instruction carefully to ensure that testing is conducted only where it is ethical, proportionate, and likely to produce meaningful results.
Conclusion
Professor Grubin’s article reinforces a principle that should guide all professional polygraph practice: the polygraph is not a magical lie detector. Its value lies in the structured methodology, the quality of the questions, the expertise of the examiner, and the care taken in interpreting and reporting the results.
When used responsibly, polygraph testing can support disclosure, inform risk assessment, and contribute to evidence-led decision-making across a range of forensic, legal, clinical, and investigative contexts. When used poorly — without appropriate question design, professional interpretation, or ethical safeguards — it risks producing misleading results that serve no one.
Dr Keith Ashcroft and the Centre for Forensic Neuroscience are committed to delivering polygraph examinations that meet the highest professional standards — carefully structured, transparently reported, and always interpreted within the appropriate forensic context.
Source
- Grubin, D. — The Polygraph and Forensic Psychiatry. Journal of the American Academy of Psychiatry and the Law, Volume 38, Issue 4, 2010, pp. 446–451. Available at: jaapl.org/content/38/4/446
Dr Keith Ashcroft is a Consultant Investigative Psychologist and Forensic Polygraph Consultant at the Centre for Forensic Neuroscience. The Centre provides confidential, structured polygraph examinations and credibility assessments for legal, corporate, and private clients. To discuss whether a polygraph examination may be appropriate for your matter, contact Dr Ashcroft for a confidential consultation.