“Do You Solemnly Swear or Affirm?” Investigating Oath Swearing and its Effects on a Mock Rape Trial

Within U.S. courts, witnesses are given the ability to choose between declaring an oath (religious connotation) or affirmation (secular connotation) when swearing in. Given the large religious presence and prejudice toward non-believers within the U.S., we employed a brief vignette study and a mock juror experiment to explicitly measure how oath vs. affirmation choice affects perceptions of witnesses and legal judgments of victims and defendants in a rape case. For this two-part pre-registered study, we recruited U.S. jury-eligible adults (Study 1, N = 451; Study 2, N = 122) via Prolific. In Study 1, participants indicated the probable level of religiosity of hypothetical court witnesses who chose to swear an oath or give an affirmation. In Study 2, participants read a mock trial transcript summary in which the victim and defendant took an oath or affirmation. Then they rendered a verdict and provided ratings for various perceived characteristics of the victim and defendant. Results from Study 1 showed that participants perceived the oath-swearing witness as more religious, those who chose the oath themselves were actually more religious, and participants associated oath swearing with credibility. Results from Study 2 reaffirmed that the oath is associated with religiosity, as participants viewed the victim taking the oath as more religious. However, oath vs. affirmation choice did not impact verdicts nor ratings of the victim and defendant. Our findings provide insight into perceived religiosity in courtroom settings. We consider implications for oath and affirmation declarations, the rape literature, and legal decision-making.