How to Detect Concealed Crime Knowledge in Situations With Little Information Using the Forced Choice Test

The Forced Choice Test (FCT) can be used to detect concealed crime knowledge, but it requires more evidence than typically available from a crime to be constructed. We propose a method to repeat individual pieces of evidence to achieve the necessary test length, hence widening the practical applicability. According to our method, FCT trials are created so that on each trial examinees are presented with a novel and unique decision between two answer alternatives even if a specific piece of information is presented again. We argue that if the decision in each trial is unique, the properties and diagnosticity of a traditional FCT can be maintained. In experiment 1, we provide a proof of concept by comparing our novel method with a traditional FCT and demonstrate that an FCT with repeated presentation of the same evidence has diagnostic value (AUC = .69) albeit less so than a traditional FCT (AUC = .86). In experiment 2, we put our novel FCT to the test in a situation with insufficient information for a traditional FCT alongside the Concealed Information Test (CIT), which also detects concealed information but relies on psychophysiological indices. Both, the FCT (AUC = .81) and CIT (AUC = .83) were diagnostic and combining them increased the detection accuracy even further (AUC = .91). If replicated, our novel FCT increase practical applicability of the FCT in general and in conjunction with the CIT.