The Devil's Advocate Approach to Detect Lying about Opinions

The Devil’s Advocate Approach is an interview protocol aimed at detecting lying about opinions. In the Devil’s Advocate approach, interviewees are first asked to explain the reasons why they have a certain opinion (eliciting-opinion request). They are then asked to play devil’s advocate and to give reasons that go against their opinion (devil’s-advocate request). Truth tellers should find it easier to respond to the eliciting-opinion request than to the devil’s-advocate request. Arguments that support someone’s attitude (eliciting-opinion request) are typically more readily available than reasons that oppose someone’s attitude (devil’s-advocate request) (Ajzen, 1991). For lie tellers, the devil’s-advocate request is an invitation to give their true opinion and the arguments should be readily available to them. Yet, lie tellers’ results are unlikely to show the opposite pattern to truth tellers’ results, because lie tellers will be motivated to use at least two counter-interrogation strategies: Preparation and consistency (Deeb et al., 2018). Lie tellers will think prior to the interview about arguments they can present that support their pretended opinion. This should improve the eloquence of their replies to the eliciting-opinion request (eloquence is the collective term for plausibility, immediacy, and clarity). Lie tellers typically strive to be consistent (Deeb et al., 2017; Vrij et al., 2021). Consistency in the Devil’s Advocate interview would mean providing replies of similar eloquence to the eliciting-opinion and devil’s-advocate requests. In the experiments published to date this pattern of results indeed emerged (Leal et al., 2010, 2023; Mann et al., 2022).

We will carry out three experiments to strengthen the veracity effects when using the Devil’s Advocate approach. The underlying principle in all three experiments is that being exposed to example responses at the beginning of the interview will have a different effect on truth tellers and lie tellers when answering the eliciting-opinion and devil’s advocate questions. Specifically, interviewees will (i) listen to a Model Statement (Experiment 1); (ii) watch a video containing pro-arguments (Experiment 2) or (iii) watch a video containing anti-arguments (Experiment 3).