A common police interview technique used to detect a lying suspect — both for the FBI and the British Police — is not reliable, according to a new study published in the Journal of Investigative Psychology and Offender Profiling.
FBI, Police lie detection method flawed, scientists say
Researchers under leadership from the University of Portsmouth completed a crucial analysis of the Model Statement lie detection technique. It raises concerns regarding the acceptance of a technique deemed dangerous when used to pursue criminal justice — with researchers calling for an urgent review of the practice, SciTech Daily reports.
Lie detection is a significant phase of criminal investigation, and are typically hard to parse — since only small and unreliable differences exist between authentic and fictional statements. This is why researchers developed interview techniques to amplify possible clues of deception and enhance the performance of lie detection techniques.
The Model Statement technique aims to elicit longer, more detailed statements because they usually offer extra clues to deception than shorter ones. While there are also other techniques, Model Statement has grown more popular.
Model Statement lie detection lacks 'theoretical underpinning'
However, while the Model Statement is promising, researchers found it is not ready for practice in any official capacity.
Cody Porter, lead researcher of the study and senior teaching fellow in psychology and offending behavior at the University of Portsmouth said: "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 marks the first time a crucial analysis of the popular Model Statement lie detection technique was carried out to completion. Porter added: "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 practice by police officers or any other investigators," Porter said.
Lie detection techniques should prompt divergent responses
At present, the Model Statement technique can do more harm to criminal investigation, since it creates an incentive for 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," said Porter.
The report also says researchers should develop tools capable of encouraging liars and non-liars to use different verbal strategies after hearing similar instructions — widening the contrast and potentially lowering false positives.
As law enforcement agencies in the U.S. come under question amid politically turbulent times, it's important to remember how tacit assumptions in and about the criminal justice system may lead to errors — ones social scientists can work to address in procedures like lie detection, and the Model Statement technique.