Adjunct Techniques

Concealed Information Tests

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• Introduction

  The Concealed Information Test (AKA Guilty Knowledge Test) is a PDD method with special capabilities not shared by either the Comparison Question Techniques or the Peak of Tension test. Concealed Information Tests (CIT) are objective, scoreable, and have a large body of accuracy research. The theory underpinning the CIT is also better established, and may be easier to defend in evidentiary examinations.

  This guide is a step-by-step instruction on how to prepare, conduct, and analyze the CIT.

• Definitions

  Alternative Item: Non-Key item in the CIT.

  Electrodermal Activity (EDA): Relatively rapid change in the electrical properties of the skin, recorded as resistance or conductance.

  False Positive Error Probability: Statistical estimation that an innocent examinee would react to the Key(s) simply by chance.

  Key: The critical item in the CIT; it is the stimulus known to the examiner as being directly related to the crime being investigated.

• Case Preparation

  The Concealed Information Test is a method to determine what an examinee knows about the details of a particular crime. Ideally, the examiner knows the details of the crime, but the CIT can also be used in a searching capacity, to uncover vital evidence not known to investigators. The first step for both applications is a review of the evidence. Below are potential sources of information for constructing the CIT.

  • Police reports
  • Witness statements
  • Victim statements
  • Crime scene photos
  • Forensic reports
  • Alibi statements

• Construction

  Each CIT should have one Key and at least five Alternative items. All items should be equally plausible to an innocent examinee. Innocent examinee should be naïve regarding the details of the crime under investigation, including the Keys. The pre-test should be used to determine what the subject already knows about the case.

  One Alternative (non-Key) item will be in the first position of the question list. The order of all others, including the Key, is random.

  It is recommended that there be at least three different Keys, to construct three CITs. Practical or fatigue factors aside, there is no maximum number of CITs that can be conducted. Accuracy improves with the number of CITs. Accuracy levels are reported between 80 and 90% depending on the number of Keys. Visual stimuli (i.e. photos) can be used instead of words for Alternative and Key items.

  Example CIT

  "If you are the person who broke into the house, you stole something. Repeat after me these items."

  1. Handgun
  2. Cash
  3. Bottle of bourbon
  4. Cellphone
  5. Necklace
  6. (Key) Laptop

• Conducting the CIT

  1. The CIT uses only EDA, though examiners should continue to record other channels as required by policy or law.
  2. Each CIT is given only one time. At the beginning of each CIT, the examiner should give a preparatory statement. The following statement may be used, filling in the parenthetical portions to match the crime: "If you are the person who (committed this crime), you would know what the (type, color, brand, caliber, etc.) was. Repeat after me each of these (types, colors, brands, calibers, etc)."
  3. Have the examinee repeat the items after you say them, rather than only answering "no." Repeating serves to verify that the examinee heard the examiner correctly, and will help prevent dissociation.
  4. Use a pace of 15 seconds
  5. Do not reveal the Key through your behavior or voice inflections.
  6. Repeat Steps 2-5 for each CIT. It is not necessary to stop between CITs.

• Interpreting the CIT

  1. If the Key elicited the largest EDA response, that test is scored a "2."
  2. If the Key elicited the second-largest EDA response, the test is scored a "1."
  3. If the Key did not elicit the largest or second-largest EDA response, the test is scored a "0."
  4. Sum the scores of all CITs.
  5. As the sum of scores increases, the probability of concealed knowledge also increases. The table below shows the likelihood of an innocent person obtaining particular scores.
  6. The three possible outcomes are: Recognition Indicated, No Recognition Indicated, and No Opinion

  Likelihood of Innocent Examinee Obtaining Scores

  Swipe to view the full table

  		Scores
  		3	4	5	6	7	8	9	10	11	12	13	14	15	16
  Number of CITs
  	2	12.0%	4.0%
  	3	28.0%	12.8%	3.2%	0.8%
  	4	43.8%	24.6%	10.1%	3.7%	0.8%	0.2%
  	5	57.7%	37.5%	19.7%	9.2%	3.2%	1.0%	0.3%	0.2%	0.0%
  	6	68.9%	49.9%	30.9%	16.9%	7.7%	3.1%	1.0%	0.3%	0.0%	0.0%
  	7	77.6%	60.9%	42.3%	26.3%	14.2%	6.8%	2.7%	1.0%	0.3%	0.1%	0.0%	0.0%
  	8	84.1%	70.2%	53.1%	36.4%	22.2%	12.2%	5.8%	2.5%	0.9%	0.3%	0.1%	0.0%	0.0%	0.0%

  The numbers along the left of the table are the number of CITs. The numbers along the top are the scores. Using this table, one can calculate the likelihood that an innocent person would obtain a given score or higher. For example, if there were 4 CITs conducted, and the total score was 6, the probability of an innocent person obtaining this score would be 3.7%. In other words, with this score an examinee's claim of ignorance of crime details is probably untrue. Scores in italics indicate probabilities are less than 5%. Bold indicates likelihoods between 5% and 30%.