Aim:

We examined the ability to detect lying about opinions with the Devil's Advocate Approach and Verifiability Approach.

Method:

Interviewees were first asked an opinion eliciting question to argue in favour of their alleged personal view. This was followed by a devil's advocate question to argue against their alleged personal view. Since reasons that support rather than oppose an opinion are more readily available in people's minds, we expected truth tellers' responses to the opinion eliciting question to include more information and to sound more plausible, immediate, direct, and clear than their responses to the devil's advocate question. In lie tellers these patterns were expected to be less pronounced. Interviewees were also asked to report sources that could be checked to verify their opinion. We expected truth tellers to report more verifiable sources than lie tellers. A total of 150 participants expressed their true or false opinions about a societal issue.

Results:

Supporting the hypothesis, the differences in plausibility, immediacy, directness, and clarity were more pronounced in truth tellers than in lie tellers (answers to eliciting opinion question sounded more plausible, immediate, direct, and clear than answers to the devil's advocate question). Verifiable sources yielded no effect.

Conclusions:

The Devil's Advocate Approach is a useful tool to detect lies about opinions.