NDI

What Is NDI?

NDI (No Deception Indicated) is a polygraph result classification. A diagnostic opinion indicating that physiological data from the polygraph examination shows no significant responses suggestive of deception to relevant test questions. The examinee's strongest responses were to comparison questions rather than relevant questions. NDI is used in single-issue diagnostic testing only.

Understanding Polygraph Results

Polygraph results are determined through validated Test Data Analysis methods that quantify the physiological response patterns recorded during the examination. For single-issue diagnostic tests, results are classified as Deception Indicated, No Deception Indicated, or Inconclusive. For multi-issue screening tests, the terminology shifts to Significant Response or No Significant Response.

The classification is based on empirically derived cut-scores that determine where the boundary falls between deception and truthfulness, balancing sensitivity (detecting deception) against specificity (protecting truthful examinees from false accusations). Research shows that validated techniques achieve accuracy rates exceeding 90% for specific-issue diagnostic testing.

Context and Interpretation

Polygraph results should always be interpreted in context. Factors including the testing technique, scoring method, data quality, and examinee suitability all influence the confidence that can be placed in any individual result. Quality control review by a second qualified examiner is recommended to strengthen the reliability of the diagnostic opinion.

Related Terms

Understanding NDI in context requires familiarity with several related polygraph concepts:

See also: DI, Diagnostic Opinion, False Negative, False Positive, Field Study, Hyperreactivity.

Further Reading

For more information on polygraph terminology and the science of lie detection, explore the full Polygraph Glossary with over 250 defined terms. Visit the Polygraph Examiner Hub for professional resources, the research database for published polygraph studies, or learn how a polygraph works if you are preparing for an examination.

Key Takeaways

NDI is an important concept within the field of Psychophysiological Detection of Deception. Whether you are a polygraph examiner, student at an APA-accredited training program, legal professional evaluating polygraph evidence, or a private individual preparing for a lie detector test, understanding this term and its relationship to other polygraph concepts will help you navigate the field with greater confidence and knowledge.

The science of polygraph testing has evolved significantly over more than 100 years, from the early work of William Moulton Marston and Leonarde Keeler to today's digital instruments and validated scoring algorithms. Every term in this glossary represents a piece of that scientific and professional heritage. For a comprehensive overview, visit the Polygraph Examiner Hub or use our examiner selection guide to find a professional examiner near you.