Several government agencies use the Hillen Credibility Factors to help their investigators and decision makers assess the veracity and credibility of a subject’s statement, particularly in instances where there is one person’s word against another’s and there is no independent corroborating evidence. These Hillen credibility factors come from a decision of the Merit Systems Protection Board in 1987 from their decision on the case: Hillen v. Dept. of the Army, 35 MSPR 453 (1987). From the opinion*:

To resolve credibility issues, an administrative judge must first identify the factual questions in dispute; second, summarize all of the evidence on each disputed question of fact; third, state which version he or she believes; and, fourth, explain in detail why the chosen version was more credible than the other version or versions of the event. Numerous factors, which will be considered in more detail below, must be considered in making and explaining a credibility determination. These include: (1) The witness's opportunity and capacity to observe the event or act in question; (2) the witness's character; (3) any prior inconsistent statement by the witness; (4) a witness's bias, or lack of bias; (5) the contradiction of the witness's version of events by other evidence or its consistency with other evidence; (6) the inherent improbability of the witness's version of events; and (7) the witness's demeanor.

1. The Opportunity and Capacity to Observe the Event or Act.
   Personal knowledge of the event or act at issue is an essential qualification of a witness, and the requisite personal knowledge is established by evaluation of the witness's opportunity, as to place, time, proximity, and similar factors, to observe the event or act in issue. These factors relating to a witness's opportunity to observe are material in determining the witness's credibility. The witness's capacity to observe refers to his or her ability to understand what was seen and intelligently narrate it.
   
   
2. Character.
   Character evidence may be used for impeachment of a witness on the theory that certain characteristics render that person more prone to testify untruthfully.
   
   
3. Prior Inconsistent Statement.
   The effect of a prior inconsistent statement is not that the present testimony is false but that the very fact of the inconsistency raises doubt as to the truthfulness of both statements. The form of the inconsistency, whether oral, in writing, or by conduct, is immaterial and the statements or conduct need not be in direct conflict. Inconsistencies, however, do not necessarily render testimony incredible.
   
   
4. Bias.
   The possibility of bias is always significant in assessing a witness's credibility. Bias rests on the assumptions that certain relationships and circumstances impair the impartiality of a witness and that a witness who is not impartial may consciously or unconsciously shade his or her testimony for or against one of the other witnesses or parties. The trier of fact must be sufficiently informed of the underlying relationships, circumstances, and influences operating on the witness, so that in the light of his or her experience, he or she can determine whether a mutation in the testimony could reasonably be expected as a probable human reaction.
   
   One aspect of bias is the question of self-serving testimony. Although the fact that a witness's testimony may be self-serving does not by itself provide sufficient grounds for disbelieving that testimony, it is a factor for consideration in assessing the probative weight of the evidence.
   
   
5. Contradiction by or Consistency with Other Evidence.
   Contradiction is the calling of one or more witnesses who deny the fact or facts asserted by another witness and maintain that the opposite is the truth; the contradiction in itself does nothing probatively unless the contradicting witness or witnesses is believed in preference to the first witness. Contradiction rests on the inference that if a witness is mistaken about one fact, he or she may be mistaken about more facts and therefore his or her testimony is untrustworthy. On the related topic of polygraph evidence, the Board has previously stated that the admissibility of polygraph results is a matter within the authority of the administrative judge. In finding polygraph results admissible, the Board does not imply that the results of such a test must be accepted into evidence.
   
   

Inherent Improbability.
Inherent improbability relies on the trier of fact's evaluation of the likelihood of the event occurring in the manner described in the testimony.

Demeanor.
Demeanor constitutes the carriage, behavior, manner, and appearance of a witness during testimony. Assessment of demeanor depends upon direct observation of the witness during his or her testimony, and, therefore, necessarily depends on demeanor findings made by the administrative judge.

The Hillen case involved allegations from five female employees at the command that a Senior Executive Service official of the Military Traffic Management Command (MTMC) sexually harassed them at work.

Exceptions

Research has demonstrated that brain functions and memory of victims of trauma, such as a sexual assault, are significantly affected by the event, and may not follow the “traditional” indications of credibility assessments. For example, oftentimes trauma victims do not remember events in a linear, chronological order or remember many of the “secondary” details. Their memories are focused on those details of things that presented the most significant threat to their well being at the time of the incident – such as the weapon the perpetrator was holding versus the color of the vehicle he was driving. Consequently, the criteria as described above should be used with caution when applied to victims of trauma. See the January/February 2019 Investigator Tip which discusses the Forensic Experiential Trauma Interview in some detail.


* Please note that case citations in the opinion that support the various points can be found in the full decision at https://1.next.westlaw.com/Link/Document/FullText?findType=Y&serNum=1987151913&pubNum=0000909&originatingDoc=I9f064f2c549611db8ac4e022126eafc3&refType=CA&originationContext=document&transitionType=DocumentItem&contextData=(sc.DocLink)