Who Can't Keep their Stories Straight: A Cue to Deception?

Tonight in Ferguson, Missouri, Darren Wilson, the white police officer who shot and killed the unarmed Black man, Michael Brown, walked away from any charges. The grand jury made its decisions, and no files were charged. As I listened to the prosecutor's lengthy statement, my ears perked up when he mentioned the importance of the consistency of the witnesses' statements. Some, he said, were consistent over time, and others were not. The clear implication was that the inconsistent statements were lies.

I remembered that two Swedish researchers, Pars Anders Granhag and Leif Stromwall, have conducted research on the topic of the relative consistency of statements over time, depending on whether the statements were made by witnesses who were lying or telling the truth. In their research, participants watched a staged event involving a robbery and a stabbing. The witnesses, who lied or told the truth about that they had watched, had time to plan their statements. Over a period of 11 days, they were each questioned three different times about what they had witnessed.

I'm not going to review the actual research reports in detail (as I usually do) because I want to get this out in a timely manner as so many people ponder the Ferguson decision. So I'm just going to quote what the authors have to say about what they found:

1. People who viewed all three interviews were no more accurate at knowing which witnesses were lying and which were telling the truth than those who watched only the first interview.
2. Of all the people who watched the three statements, 60% said that they used the consistency of the statements to decide whether the witnesses were truthful. (If they thought the three statements were consistent, they thought the witness was truthful.)
3. Of those 60% who used consistency as their criterion for truthfulness, "half perceived the three statements to be consistent over time, whereas the other half perceived the same three statements to be inconsistent over time."
4. Most importantly, the authors noted: "when comparing truthful and deceptive consecutive statements we found them to be equally consistent." [my emphasis]

Why might liars give statements that are just as consistent over time as those of truthtellers? There are a number of possibilities. One suggested by the authors is that "liars will try to repeat what they have said in previous interrogations…, while truth-tellers will try to reconstruct what they at some point in time actually experienced."

There are important ways in which the controlled research studies were not analogous to what happened in Ferguson. So we need to be cautious in the implications we draw from the findings. What we can say, though, is people's intuitive ideas about how liars behave are not always supported by systematic research. That's so not just for laypersons, but also for professionals such as judges and police officers.

[For more of my blog posts and books on deceiving and detecting deceit, click here. And, for some totally good news about singles, check out The Secretary of State Takes on Singlism, in Prime Time.]

References

Granhag, P. A., & Stromwall, L. A. (1999). Repeated interrogations – stretching the deception detection paradigm. Expert Evidence, 7, 163-174.

Granhag, P. A., & Stromwall, L. A. (1999). Repeated interrogations: Verbal and non-verbal cues to deception. Applied Cognitive Psychology, 16, 243-257.