Human Lie-Detection Performance: Does Random Assignment versus Self-Selection of Liars and Truth-Tellers Matter?

Deception research has been criticized for its common practice of randomly allocating senders to truth-telling and lying conditions. In this study, we directly compared receivers’ lie-detection accuracy when judging randomly assigned versus self-selected truth-tellers and liars. In a trust-game setting, senders were instructed to lie or tell the truth (random assignment; n = 16) or were allowed to choose to lie or tell the truth of their own accord (self-selection; n = 16). In a sample of receivers (N = 200), we tested two alternative hypotheses, predicting opposite effects of random assignment (vs. self-selection) on receivers’ lie-detection accuracy. Accuracy rates did not differ significantly as a function of veracity assignment, failing to support the claim that random assignment of liars and truth-tellers alters the detectability of deception. Equivalence tests indicated that, while a small effect of random assignment cannot be ruled out, moderate (or larger) effect sizes are unlikely.