Just how good are police officers at detecting liars?

By Emma Barrett, of Psychology and Crime News and the Deception Blog.

We had just sat through a presentation by a proponent of the Reid Technique, a potentially psychologically coercive method of persuading a suspect to confess, used widely in North America (although not in the UK). The North American police officers, in the majority at this international conference a couple of years ago, loved it. British police delegates and we psychologists shifted uncomfortably in our seats.

Next up, an esteemed American psychology professor, who gave a tour de force of his specialist subject: false confessions. In the Reid Technique, once an officer is convinced that a suspect is guilty, the psychological coercion begins. The professor argued that this might cause a vulnerable and innocent suspect to make a false confession: much depends on whether the officer is right when they believe that a suspect claiming innocence is lying. The speaker cited a recent meta-analysis (DePaulo et al., 2003) to make the point that, according to psychological research, there are no reliable cues to deception, and added that other research implies that police officers are not very good at spotting liars. The Brits and psychologists smiled again.

But I was still uncomfortable. DePaulo’s review is great, but if you take a look at the list of studies included, you’ll find that the evidence is almost wholly from studies of how Western students behave when deceiving in relatively low-stakes situations. Research on whether
law enforcement officers can detect deception usually involves them sitting in front of video clips of, you guessed it, Western students. So, satisfying as it might be to trounce the Reid guys, shouldn’t we wait for more ecologically valid studies before we tell officers they are no good at detecting deception?

This is why I’ve chosen a recent paper from Aldert Vrij, Samantha Mann and their colleagues at Portsmouth University, published earlier this year in Applied Cognitive Psychology. Not because it’s the best paper of the last three years in forensic psychology, but because it’s the latest in a series of studies that are becoming increasingly ecologically valid and relevant to law enforcement concerns. An issue that I think is crucially important.

In this study, the materials were clips from real suspect interviews where ground truth was known, the stakes were high, and the participants were experienced police officers. A welcome step forward from the usual student-based studies.

The officers’ task was to judge four sets of clips of liars / truth tellers on four different occasions. Their total accuracy (four tests combined) was 72 per cent. This is an improvement on the usual 50-60 per cent hit rate typically found in deception studies (e.g., Vrij, 2000). Officers were equally good at detecting truth (70 per cent accuracy) and lies (73 per cent). However, on average officers believed that they had only performed at chance level, and were “overly modest about, rather than overconfident in, their performance”.

So perhaps police officers aren’t as bad at detecting deception as some might have you believe. We’ve a long way to go yet – for instance, there’s plenty of evidence that would-be lie catchers often rely on rigid cues, including signs of nervousness, which could be displayed by an innocent person who is anxious about being believed (Ekman, 2002). We need to know more about the circumstances under which this occurs – and how to stop it. But the sorts of studies that Vrij et al. are now conducting are, I think, the right way to go. Conducting such research is more challenging than doing experiments with students, but it’s a crucial step towards really helping law enforcement deal with deception. Finally, I’d like to give a big cheer to Kent Police who facilitated the research. Collaboration between academics and practitioners is by far the best – perhaps the only – way to go forward here.
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DePaulo, B.M., Lindsay, J.J., Malone, B.E., Muhlenbruck, L., Charlton, K. & Cooper, H. (2003). Cues to Deception. Psychological Bulletin, 129, 74–118.

Vrij, A., Mann, S., Robbins, E. & Robinson, M. (2006) Police officers ability to detect deception in high stakes situations and in repeated lie detection tests. Applied Cognitive Psychology 20, 741–755.

Vrij, A. (2000). Detecting lies and deceit: The psychology of lying and its implications for professional practice. Chichester: John Wiley and Sons.

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