This guidance post is written for members of the public who have undergone, or are considering, a polygraph examination. It explains what a legitimate examination looks like so that you can assess whether a service you received — or are being offered — meets recognised professional standards. The standards referenced throughout are the British Polygraph Society (BPS) Standards of Practice (v1.0, 2026) and Code of Ethics (v1.0, 2026); full citations appear in the Sources list.
Key Points
- A polygraph test is a psychophysiological examination comprising three distinct phases — pre-test interview, in-test data collection, and data analysis — and should take a minimum of 90 minutes.[1]
- A minimum of five sensor channels must be attached during data collection: two pneumograph components (thoracic and abdominal), electrodermal activity, cardiovascular, and an activity sensor.[2]
- You must give informed written consent before any testing begins, and all test questions must be reviewed with you in advance.[3]
- Results fall into defined categories — DI, NDI, INC, or NO (diagnostic); SR, NSR, INC, or NO (screening) — and an inconclusive result is always a valid outcome.[4]
- Fees must never be contingent on the outcome of the examination, and all fee arrangements should be agreed in writing beforehand.[5]
What Is a Polygraph Test?
A polygraph examination is a psychophysiological test. It measures changes in physiological activity — breathing, sweat-gland behaviour, cardiovascular function, and movement — while the examinee answers a structured set of questions.[6] The instrument does not directly detect lies. Instead, a trained examiner uses validated techniques to compare physiological responses to different categories of question and then renders a professional opinion about whether deception is indicated.
The popular term “lie detector” is therefore something of a misnomer. The polygraph records physiological data; it is the combination of a validated test technique, proper sensor placement, and a systematic data-analysis method that produces a diagnostic opinion. Only techniques whose evidentiary accuracy meets or exceeds a 90 per cent threshold satisfy BPS requirements for diagnostic (single-issue) use.[7]
The Three Phases, Step by Step
A properly conducted polygraph examination always proceeds through three sequential phases. No phase may be omitted, and all three must be conducted in person.[8]
Phase 1 — Pre-Test Interview
Before any sensors are attached, the examiner should:
- Explain the purpose of the examination, the process that will be followed, and the sensors that will be used.
- Obtain your informed written consent, which must cover the process, sensor placement, the recording, the issues under examination, and how results will be reported.[9]
- Review every test question with you before the in-test recording begins. You should know exactly what you will be asked; there must be no surprise questions.[10]
- Discuss the background to the issue under examination so that you and the examiner share a clear understanding of what each question means.
The pre-test interview is typically the longest phase. It ensures the examinee is physically and mentally prepared, and it enables the examiner to formulate questions that are clear, unambiguous, and directly relevant to the matter at hand.
Phase 2 — In-Test Data Collection
During this phase, the examiner attaches the polygraph sensors (described below) and conducts several “charts” — recorded presentations of the approved question sequence. The examination must be conducted neutrally; the examiner should display no bias regarding the expected outcome.[11] Throughout data collection, an audio or audio-video recording must be maintained.[12]
The examiner must use a validated, evidence-based technique.[13] This means the question format, the order of questions, and the number of chart presentations all follow a protocol that has been studied and shown to produce reliable results.
Phase 3 — Data Analysis
After data collection, the examiner analyses the recorded physiological data using a validated scoring method.[14] Analysis may involve numerical scoring of response features, and the result is expressed as a formal opinion. The result is not final until it has been documented in a written examination report.[15]
Sensors and Minimum Instrumentation
A legitimate polygraph examination requires, at minimum, the following sensor channels:[16]
| Sensor | What It Measures | Typical Placement |
|---|---|---|
| Thoracic pneumograph | Upper chest breathing patterns | Rubber tube or electronic sensor around the chest |
| Abdominal pneumograph | Lower (diaphragmatic) breathing patterns | Rubber tube or electronic sensor around the abdomen |
| Electrodermal activity (EDA) sensor | Sweat-gland activity on the skin surface | Two small electrodes on the fingers or palm |
| Cardiovascular sensor | Relative blood pressure and pulse rate changes | Blood-pressure cuff on the upper arm or similar transducer |
| Activity sensor | Movement or muscular pressure | Seat pad, arm-rest sensors, or similar |
If an examiner uses fewer than these five sensor channels, the examination does not meet the minimum standard. The sensors are non-invasive and should cause no pain, though the cardiovascular cuff may feel tight during chart collection.
Understanding Your Results
Polygraph opinions are expressed using specific professional terminology. The categories differ depending on whether the examination is diagnostic (single-issue, addressing one specific allegation) or a screening examination (addressing a broader topic area).
Diagnostic (Single-Issue) Opinions
| Abbreviation | Meaning | Explanation |
|---|---|---|
| DI | Deception Indicated | The physiological data, when analysed with a validated method, indicate that the examinee’s responses to the relevant questions are consistent with deception. |
| NDI | No Deception Indicated | The data indicate that the examinee’s responses are not consistent with deception. |
| INC | Inconclusive | The data do not meet the threshold for either a DI or NDI opinion. This is a valid result and must be reported as such. |
| NO | No Opinion | The examiner is unable to render a diagnostic opinion, typically because of a procedural or data-quality issue. |
Screening Opinions
| Abbreviation | Meaning |
|---|---|
| SR | Significant Response — responses of concern identified |
| NSR | No Significant Response — no responses of concern identified |
| INC | Inconclusive — data insufficient for either opinion |
| NO | No Opinion |
What Results Do Not Mean
A polygraph opinion is not a statement of guilt or innocence. It is a professional assessment of whether the physiological data are consistent with deception in relation to specific questions. An examiner must not overstate the reliability of results.[18] Equally, a DI result does not mean you are definitely lying, and an NDI result does not constitute absolute proof of truthfulness. Results should always be considered alongside other information available to the decision-maker.
Your Rights as an Examinee
If you are taking a polygraph examination voluntarily (i.e., not under a statutory obligation administered by HMPPS), you have the following rights. For a fuller treatment, see Your Rights.
- Informed consent. You must be given a full explanation of the process, the sensors, the recording, the issues to be examined, and how results will be reported — and you must give written consent before testing begins.[19]
- Question review. Every question to be asked during the examination must be reviewed with you beforehand.[20]
- Confidentiality. All information relating to your examination is confidential and may be released only to the persons identified in your written consent.[21]
- Data protection. Your examiner must comply with the UK General Data Protection Regulation (UK GDPR) and the Data Protection Act 2018.[22]
- No discriminatory questions. Questions relating to protected characteristics under the Equality Act 2010 may not be asked unless directly relevant and with your written consent.[23]
- Written report. Your result is not final until documented in a written examination report.[24]
- No conflict of interest. The examiner must not have a dual role with you (for example, acting as both therapist and examiner) and must be free from conflicts of interest.[25]
Red Flags of Illegitimate Practice
Warning Signs to Watch For
Not all individuals or companies offering polygraph services operate to recognised professional standards. The following indicators should cause concern.
| Red Flag | Why It Matters | Relevant Standard |
|---|---|---|
| No informed consent form | Informed written consent is a fundamental requirement. Without it, the examination lacks a proper basis and your rights are unprotected. | BPS Standards of Practice §7.2[26] |
| No question review | If you are not shown every question before the recording begins, you cannot provide genuinely informed consent and the test methodology is compromised. | BPS Standards of Practice §7.3[27] |
| Examination lasts less than 90 minutes | A proper examination — covering all three phases — requires a minimum of 90 minutes. A substantially shorter session suggests corners are being cut. | BPS Standards of Practice §8.10[28] |
| No audio or video recording | Recording protects both examiner and examinee. Without it, there is no independent record of what occurred during the session. | BPS Standards of Practice §8.5[29] |
| Result given verbally only, with no written report | A result is not final until it is documented in writing. A verbal-only result may be unreliable, may change, and leaves you with no evidence of what was found. | BPS Standards of Practice §10.5[30] |
| Examiner lacks current APA certification | BPS members are required to maintain current American Polygraph Association (APA) certification. An examiner without such certification may lack the training and continuing education necessary for competent practice. | BPS Code of Ethics §8.3[31] |
| Examiner pressures you about the result | The examination must be conducted neutrally, without bias. Pressuring an examinee to make admissions or accept a result is unprofessional and undermines validity. | BPS Standards of Practice §7.4[32] |
| Fee is contingent on the outcome | “Pay only if you pass” arrangements are expressly prohibited. They create a financial incentive that undermines examiner neutrality. | BPS Code of Ethics §3.2[33] |
| False or misleading advertising | Examiners must not make false claims about their qualifications, the accuracy of the technique, or the services offered. | BPS Code of Ethics §5.1[34] |
Important
The presence of one or more of these red flags does not automatically mean the result is wrong, but it does indicate that the examination may not meet the standard required for reliable, ethical practice. If you have concerns, consider seeking independent advice or a second opinion from a properly qualified examiner.
How to Check Whether Your Examiner Is BPS-Listed
The BPS maintains an examiner directory of its current members. You can use this directory to verify whether a particular practitioner holds BPS membership. Membership of the BPS indicates that the examiner has agreed to abide by the Society’s Standards of Practice and Code of Ethics and is subject to its complaints and discipline procedures.
A Note on the Scope of BPS Membership
The BPS is a UK membership body and binds only its own members. It is not a statutory regulator and does not license or regulate all polygraph practitioners in the United Kingdom. The statutory polygraph regime in England and Wales (applying to certain sexual and domestic-abuse offenders) is administered by HMPPS under the Offender Management Act 2007 (ss.28–30) and Domestic Abuse Act 2021 (s.76); BPS has no role in that regime. Not all competent examiners in the UK are BPS members; however, BPS membership provides one verifiable route to confirming an examiner’s adherence to a published set of professional standards.
How to Complain About Poor Service
If you have received a polygraph examination from a BPS member and believe it fell short of the standards described in this guide, you may submit a complaint under the BPS Complaints, Discipline and Appeals Procedure. Any breach of the Standards of Practice or Code of Ethics by a BPS member is subject to investigation under this procedure.[35]
If the examiner is not a BPS member, the BPS has no jurisdiction over them. In that case, you may wish to consider:
- Complaining directly to the individual or company concerned.
- Contacting the American Polygraph Association (APA) if the examiner holds APA certification, as the APA has its own ethics and grievance process.
- Seeking legal advice if you believe you have suffered harm or loss.
- Contacting the Information Commissioner’s Office (ICO) if you believe your data has been mishandled in breach of UK GDPR or the Data Protection Act 2018.
Glossary
- APA
- American Polygraph Association — the principal international professional body for polygraph examiners. BPS members are required to maintain current APA certification.
- BPS
- British Polygraph Society — a UK membership body, founded in 2017, for polygraph examiners practising in the United Kingdom. It publishes professional standards and a code of ethics binding on its members.
- CPD
- Continuing Professional Development — structured learning activities that professionals undertake to maintain and update their skills and knowledge.
- DI
- Deception Indicated — a diagnostic opinion meaning the physiological data are consistent with deception on the relevant questions.
- DPA 2018
- Data Protection Act 2018 — the UK statute that supplements and implements the UK GDPR, governing the processing of personal data.
- EDA
- Electrodermal Activity — changes in the electrical properties of the skin caused by sweat-gland activity, measured at the fingers or palm during a polygraph examination.
- HMPPS
- His Majesty’s Prison and Probation Service — the executive agency of the Ministry of Justice responsible for, among other things, the statutory polygraph programme for certain offenders in England and Wales.
- INC
- Inconclusive — a result indicating that the physiological data do not meet the threshold for either a Deception Indicated or No Deception Indicated opinion. It is a valid and reportable outcome.
- NDI
- No Deception Indicated — a diagnostic opinion meaning the physiological data are not consistent with deception on the relevant questions.
- NO
- No Opinion — the examiner is unable to render a diagnostic or screening opinion, typically due to a procedural or data-quality issue.
- NSR
- No Significant Response — a screening opinion meaning no physiological responses of concern were identified.
- PCSOT
- Post-Conviction Sex Offender Testing — a specialised application of polygraph used in the management and treatment of convicted sexual offenders, requiring 40 hours of additional training beyond basic polygraph education.
- Pneumograph
- A sensor that records breathing patterns. A legitimate polygraph examination uses two pneumograph channels — one for the chest (thoracic) and one for the abdomen.
- SR
- Significant Response — a screening opinion meaning physiological responses of concern were identified on one or more screening topics.
- UK GDPR
- United Kingdom General Data Protection Regulation — the retained-EU regulation governing the processing of personal data in the UK, forming part of UK data protection law alongside the DPA 2018.
Sources
- British Polygraph Society (2020). Standards of Practice, v1.0. Available at: polygraph.org.uk/standards-ethics/standards-of-practice/.
- British Polygraph Society (2020). Code of Ethics, v1.0. Available at: polygraph.org.uk/standards-ethics/code-of-ethics/.
This post is a guidance document published by the British Polygraph Society for informational purposes. It does not constitute legal advice. The standards described are those to which BPS members are bound; they do not apply to non-members or to the statutory polygraph programme administered by HMPPS. If you require legal advice about a polygraph examination or its results, you should consult a qualified solicitor. If you believe you have received substandard service from a BPS member, the Society’s Complaints, Discipline and Appeals Procedure is available.