Behavioral Cues and Credibility

Experienced investigators pay attention to behavior. They notice changes in tone, posture, eye contact, speech and engagement. Those observations can help an interviewer recognize that a subject is uncomfortable, confused, distracted or having difficulty discussing a particular subject.

The difficulty comes when an observation is treated as proof of why the behavior occurred. A person who looks away may be nervous, embarrassed, thinking, culturally uncomfortable with prolonged eye contact or simply tired. A long pause may reflect deception, but it may also mean that the person is searching their memory, trying to understand the question or deciding how to describe a difficult experience.

Behavior may tell the interviewer that something changed. It generally does not explain why it changed.

The Limits of Behavioral Cues

Some interview training has historically associated behaviors such as gaze aversion, fidgeting, changes in posture, hesitations and variations in vocal tone with deception. Research has not established that these behaviors allow an interviewer to reliably determine whether a particular person is lying.

A large review of the research concluded that the nonverbal cues associated with deception tend to be faint and unreliable. Another analysis involving more than 200 studies found that people correctly classified truthful and deceptive messages approximately 54 percent of the time. That result is slightly better than chance, but it is not sufficiently accurate to support important investigative conclusions about an individual.

This does not mean that behavior is meaningless. It means that the same behavior can have several plausible explanations and should not be assigned a single meaning without additional information.

What About Clusters of Behavior?

Interviewers are sometimes advised not to rely on one behavior but to look for several behaviors appearing together. Considering the complete context is better than making a decision from one isolated movement. However, calling several observations a “cluster” does not automatically make the resulting conclusion reliable.

A specific combination of behaviors would need to be validated before it could support a meaningful claim about deception. Combining several ambiguous behaviors does not, by itself, establish why the person displayed them.

A change in behavior may justify a follow up question. It should not, standing alone, justify labeling someone deceptive.

A Better Use of Behavioral Observations

Behavioral observations can still help an interviewer manage the conversation. If a subject appears confused, the interviewer can rephrase the question. If the person becomes withdrawn, the interviewer can slow down, revisit rapport or ask whether something is making the conversation difficult. If the subject appears fatigued, a break may improve the quality of the information obtained.

This approach uses behavior to inform communication without turning it into a lie detection system.

When documenting an interview, it is also more accurate to describe what occurred than to assign a conclusion to it. For example, “The subject paused for approximately 15 seconds before answering” is an observation. “The subject displayed deceptive behavior” is an interpretation that the observation alone cannot establish.

Evaluating the Account

Credibility should be evaluated through the information gathered during the interview and the investigation as a whole. Useful practices include:

• Allowing the person to provide an uninterrupted account
• Asking open ended questions before moving to specific questions
• Clarifying unclear or apparently inconsistent information
• Identifying details that can be independently verified
• Comparing the account with reliable evidence
• Considering reasonable alternative explanations
• Remaining open to information that does not support the investigator’s original theory

Contradictions and inconsistencies deserve careful follow up, but they are not automatically proof of deception. People can provide inconsistent information because of faulty memory, misunderstanding, fear, trauma, intoxication, the passage of time or the manner in which questions were asked. The investigator’s job is to explore the discrepancy and determine whether it can be resolved or independently corroborated.

Experience and Research Can Work Together

Current research does not require investigators to stop observing people or disregard their professional experience. It provides a useful warning about the limits of conclusions drawn from behavior alone.
Good investigative interviewing has always required patience, careful listening, thoughtful questions, corroboration and professional judgment. Research can help investigators use those skills while avoiding conclusions that the available information does not support.

Behavior can help an interviewer decide how to continue the conversation. Conclusions about what happened should come from the complete account, reliable evidence and the totality of the investigation.