Lie Detector Results
Lie detector results explain how a person’s physiological responses were interpreted during a polygraph examination. Results are commonly described as No Deception Indicated (NDI), Deception Indicated (DI) or Inconclusive, although terminology can vary depending on the testing technique.
A polygraph does not read minds or directly detect lies. The polygraph instrument records physiological responses while a person answers agreed questions. A trained examiner then reviews the recorded data using the appropriate scoring method.
Understanding what each result means is important because passing should not be treated as absolute proof of innocence, and failing does not automatically prove that someone lied.
What Do Lie Detector Results Mean?
During a polygraph test, the instrument records physiological changes while the examinee answers structured questions.
Depending on the equipment and testing procedure, measurements can include breathing, cardiovascular activity, blood pressure and skin conductivity.
These responses are recorded across the examination and analysed by the polygraph examiner. The result therefore comes from the complete testing process, not from one reaction or the polygraph machine making an automatic decision.
A professional examiner should explain the test results clearly and distinguish between a conclusive result and an inconclusive outcome.
What Are the Three Main Polygraph Test Results?
Polygraph results are commonly grouped into three broad outcomes.
No Deception Indicated (NDI)
No Deception Indicated means the recorded responses did not meet the criteria for deception under the testing and scoring method used.
In everyday language, this is often described as passing a lie detector test.
However, an NDI result should not be described as absolute proof that a person is innocent or that every statement they have ever made is truthful. It relates to the specific relevant questions examined during that test.
Deception Indicated (DI)
Deception Indicated means the examiner identified a response pattern that met the criteria for deception under the technique being used.
This is commonly described as failing a polygraph test.
A DI result does not automatically establish guilt or prove that someone committed an offence. Polygraph evidence should be understood within the context of the specific issue, questions and examination.
Inconclusive
An inconclusive result means the physiological data was not sufficiently clear to support a confident truthful or deceptive classification.
Inconclusive does not mean failed, nor does it mean passed.
Factors such as inconsistent physiological reactions, data quality or testing conditions may contribute to an unclear outcome. Our guide to inconclusive lie detector results explains this outcome in more detail.
How Do I Know If I Passed My Polygraph Test?
If your result is reported as No Deception Indicated (NDI), it is generally considered a passed result for the relevant questions examined.
If the result is Deception Indicated (DI), it is generally considered a failed result.
An inconclusive result is neither.
The examiner should provide a post-test explanation so you understand the terminology used and what the outcome means. You should not have to interpret raw polygraph charts yourself.
What Does a Lie Detector Result Look Like?
A lie detector result is not simply a screen displaying “true” or “false”.
During the polygraph examination, the instrument produces physiological recordings from the sensors attached to the examinee. These recordings allow the examiner to review how responses changed while specific questions were answered.
The examiner analyses the data according to the testing and scoring procedure being used and then reports the resulting classification.
At Lie Detectors UK, results are explained on the same day, and a written report is included after the examination.
The report should make the outcome understandable without requiring the client to interpret physiological recordings or technical scoring data independently.
How Are Polygraph Results Determined?
A professional polygraph examination involves more than attaching sensors and asking questions.
Pre-Test Interview
During the pre-test interview, the examiner discusses the issue being tested, explains the procedure and reviews the relevant questions.
Relevant medical, medication or other circumstances that could affect whether the examination can be conducted properly should also be discussed beforehand.
Test Questions
A standard Lie Detectors UK examination usually focuses on up to three relevant questions or statements.
Depending on the validated technique being used, relevant questions may be considered alongside comparison or control questions.
Questions should be clear and understood before physiological recording begins. There should not be surprise relevant questions during the examination.
Physiological Recording
The polygraph instrument measures physiological responses that can include breathing, cardiovascular activity, blood pressure and skin conductivity.
These physiological changes do not directly prove deception. They provide data for analysis within the structured examination.
Examiner Review
After data collection, the examiner reviews the polygraph charts and applies the appropriate scoring method.
Examiner competence matters because the result depends on recognised testing protocols, appropriate question formulation, data quality and correct interpretation.
The American Polygraph Association publishes professional standards and information relating to validated polygraph techniques, examiner education and polygraph practice.
What Is a Good Score on a Polygraph?
There is no single universal number that consumers should treat as a “good polygraph score”.
Scoring depends on the examination format and validated technique being used. Different methods may use different numerical rules or decision thresholds.
For the person taking the test, the meaningful information is usually the examiner’s final classification, such as No Deception Indicated, Deception Indicated or Inconclusive, together with an explanation of what that result means.
Raw scores should therefore not be compared across different polygraph examinations without understanding the technique used.
Can an Innocent Person Fail a Polygraph?
Yes. A truthful or innocent person can potentially receive an incorrect deceptive result.
This is known as a false positive.
The opposite can also occur. A false negative is when a deceptive person is incorrectly classified as truthful.
This is one reason polygraph results should not be treated as infallible proof.
If you are concerned about this possibility, see our guide explaining whether you can fail a lie detector test while telling the truth.
How Accurate Are Lie Detector Results?
No lie detector test is 100% accurate.
Validated polygraph techniques can achieve accuracy rates above 90% when conducted properly by a qualified examiner, although accuracy varies depending on the testing method, examiner, questions and testing conditions. Inconclusive results are also possible.
That is why claims that a lie detector can accurately detect lies in every person or situation should be treated cautiously.tail.
What Can Affect Lie Detector Test Results?
Several factors can affect a polygraph examination, including:
- poorly formulated or ambiguous questions
- unsuitable testing conditions
- relevant medical conditions
- medication
- illness or significant discomfort
- severe fatigue or lack of sleep
- excessive movement
- data quality
- examiner competence
- the testing technique used
Anxiety can also influence physiological responses, but nervousness alone does not automatically mean someone will fail.
Relevant circumstances should be disclosed during the pre-test discussion so the examiner can determine whether the examination can proceed appropriately.
What Should You Do If You Disagree With the Result?
Start by asking the examiner to explain how the result was reached.
Establish whether the outcome was DI, NDI or inconclusive and whether there were any issues with the questions, physiological data or testing conditions.
If you believe something affected the examination, raise that specific concern rather than assuming the polygraph machine simply produced the wrong answer.
A second examination may sometimes be considered, but a retest should not be treated as a guaranteed way to obtain a different result.
Someone who received a deceptive result despite answering truthfully may find our guide on why someone can fail a polygraph when telling the truth useful.
FAQs
Is a Lie Detector 100% Accurate?
No. No polygraph test is 100% accurate. Validated techniques can achieve accuracy rates above 90% when properly conducted by a qualified examiner, but false positives, false negatives and inconclusive results remain possible.
Does Passing a Polygraph Prove You Are Innocent?
No. An NDI result means deception was not indicated for the relevant questions under the testing method used. It should not be treated as absolute proof of innocence.
Does Failing a Polygraph Prove You Lied?
No. A DI result indicates that the recorded responses met the criteria for deception under the technique used, but the result is not automatic proof that a person lied or committed an offence.
How Long Does It Take to Get Lie Detector Results?
At Lie Detectors UK, results are explained on the same day. A written report is also included after the examination.
What Does an Inconclusive Result Mean?
It means the examination did not produce sufficiently clear data for a confident truthful or deceptive classification. It is neither automatically a pass nor a fail.
Conclusion
Lie detector results need to be interpreted in the context of the complete polygraph examination.
No Deception Indicated generally represents a passed result, Deception Indicated represents a deceptive or failed result, and inconclusive means the available data did not support a sufficiently clear classification.
The polygraph instrument records physiological responses rather than detecting lies directly. Question formulation, testing conditions, validated techniques and the competence of the examiner all matter when determining the result.
No polygraph test is 100% accurate. Understanding both the result and its limitations is therefore more useful than treating a pass or fail as absolute proof.