I Solemnly Swear I’m Up To Good: A Megastudy Investigating the Effectiveness of Honesty Oaths on Curbing Dishonesty

Dishonest behaviors such as tax evasion impose significant societal costs. Ex-ante honesty oaths—commitments to honesty before action—have been proposed as useful interventions to counteract dishonest behavior, but the heterogeneity in findings across operationalizations calls their effectiveness into question. We tested 21 honesty oaths (including a baseline oath)—proposed, evaluated, and selected by 44 expert researchers—and a no-oath condition in a megastudy in which 21,506 UK and US participants played an incentivized tax evasion game. Of the 21 interventions, 10 significantly improved tax compliance by 4.5 to 8.5 percentage points, with the most successful nearly halving tax evasion. Limited evidence for moderators was found. Experts and laypeople failed to predict the most effective interventions, but experts’ predictions were more accurate. In conclusion, honesty oaths can be effective in curbing dishonesty but their effectiveness varies depending on content. These findings can help design impactful interventions to curb dishonesty.