Lie detection -- Have the experts got it wrong?

October 15, 2020

A widely adopted police interview technique, used by both the FBI and British police, to spot if a suspect is lying, is not fit for use, a report out today concludes. In fact, there is evidence that the technique helps liars become even better liars.

Researchers led by the University of Portsmouth carried out a critical analysis of the Model Statement lie detection technique and the results have been published today in the Journal of Investigative Psychology and Offender Profiling. There are concerns that the use of the technique is dangerous in the pursuit of criminal justice and researchers are calling for an urgent review of its practice.

Lie detection is a vital part of any criminal investigation. Lies are typically difficult to detect, this is because only small and unreliable differences exist between genuine and fabricated statements. As such, researchers have begun developing interviewing techniques to magnify available clues to deception and improve lie detection performance. The Model Statement technique has been built on the insight that longer, more detailed statements typically contain more clues to deception that shorter statements. Although there are many different techniques used - Model Statement is becoming increasingly popular.

However, researchers have found that although the Model Statement is a promising tool for lie detection it is nowhere ready to be used in practice.

Lead researcher, Cody Porter, Senior Teaching Fellow in Psychology and Offending Behaviour, University of Portsmouth says, "In my opinion it is dangerous for Model Statement to be used in practice now because there are many sources that show that while the Model Statement technique supports truth tellers to say more it also supports liars to do the same. The outcome is that it becomes impossible to tell the difference between someone telling the truth and someone who is lying.

This is the first time a critical analysis of the Model Statement lie detection technique has been done. Porter says: As a discipline we are very good at research but we need to sometimes take a step back and look at what would actually be useful in practice."

"We argue that based on the evidence from previous studies, the mixture of different dependent measures, the diversity of Model Statement techniques in circulation, the lack of theoretical underpinning and the effects of delay on interviewees' memory performance, that the Model Statement should not be used in practise by police officers or any other investigators.

As it stands, the statement can do more harm to investigations by prompting liars to produce statements that are similar in length to truth tellers, making them appear more credible or by encouraging truth tellers to provide more information that is inaccurate."

The report proposes that researchers could instead develop tools that encourage liars and truth tellers to adapt different verbal strategies upon hearing the same instructions, thus causing their verbal behaviour to become less similar.

University of Portsmouth

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