double verification test

What Is a Double Verification Test?

The double verification test is an alternate term for a particular type of stimulation test (commonly known as the card test or numbers test) in which the examinee's known response to a controlled stimulus is verified twice — once during the test itself and once through the examiner's demonstration of the result. The term emphasises the dual nature of the verification: the polygraph verifies the examinee's concealed choice, and the examinee simultaneously verifies that the instrument can detect their deception.

How It Works

In a typical double verification test, the examinee selects a card or number that is known to them but concealed from the examiner. The examinee is then asked about each possible option while connected to the polygraph, denying knowledge of all options including the one they actually selected. The examiner then analyses the physiological data to identify which item the examinee chose.

The "double" nature of the verification refers to two simultaneous processes:

• Examiner verification — The examiner confirms the instrument is properly calibrated and recording meaningful physiological data by successfully identifying the known-lie response. This serves as a functional check of sensor placement, instrument gains, and the examinee's physiological responsiveness
• Examinee verification — The examinee witnesses first-hand that the polygraph detected their deception, establishing or reinforcing their belief in the instrument's capability. This psychological effect is crucial for the proper functioning of both comparison question and relevant question mechanisms in the subsequent diagnostic test

Psychological Function

The double verification test serves the same psychological purpose as other stimulation tests: it produces a deception exemplar and establishes the examinee's confidence (or concern) about the polygraph's detection capability. Under psychological set theory, this experience influences how the examinee distributes their psychological attention — and therefore their physiological arousal — across question types during the diagnostic portion of the examination.

For a deceptive examinee, the demonstration increases fear of detection at the relevant questions. For a truthful examinee, it reinforces concern about the comparison questions (where they may harbour some uncertainty about their own truthfulness), supporting the differential response pattern that produces a truthful result.

Variants and Terminology

The double verification test is known by several names in polygraph practice, including the card test, numbers test, known-solution test, and acquaintance test. While the specific procedures may vary slightly — some use playing cards, others use numbers written on cards, and some use a blind format where the examiner genuinely does not know the chosen item — the fundamental purpose remains the same: dual verification of the instrument's capability and the examinee's responsiveness.

Modern Practice

In contemporary validated practice, stimulation tests are a standard component of most CQT examination protocols, though the specific format and placement within the session vary by technique. The APA Standards of Practice address the use of stimulation tests as part of the overall examination protocol.