During the COVID-19 sanitary crisis, many exams were hastily moved to online mode. This revived a much needed debate over the privacy issues associated with online proctoring of exams, while the validity and fairness of unproctored exams were increasingly questioned. With a randomized control trial, we estimate the effectiveness of prior warnings as a means of discouraging academic dishonesty in exams. We use original, non-intrusive technologies to surreptitiously identify cheating in a series of unproctored assignments and send a targeted warning to half of the students who were identified as cheaters. We then compare their cheating behavior on the final exam with the behavior of the group of unwarned cheaters. The warning proves effective but does not completely eliminate cheating, as some students’ cheating strategies become more sophisticated following issuance of the warnings. We conclude that switching traditional exams to online mode should be accompanied by proctoring. When proctoring is not possible, credible and effective anti-cheating technologies should be deployed together with adequate warnings.

在 COVID-19 卫生危机期间，许多考试仓促转为在线模式。这重新引发了关于与在线监考考试相关的隐私问题的急需辩论，而无监考考试的有效性和公平性也受到越来越多的质疑。通过一项随机对照试验，我们估计了预先警告的有效性，作为阻止考试中学术不诚实的一种手段。我们使用原创的、非侵入性的技术来秘密识别一系列无监考作业中的作弊行为，并向半数被认定为作弊者的学生发出有针对性的警告。然后，我们将他们在期末考试中的作弊行为与一群未经警告的作弊者的行为进行比较。警告证明是有效的，但并不能完全消除作弊行为，随着警告的发布，一些学生的作弊策略变得更加复杂。我们得出结论，将传统考试转换为在线模式应该伴随着监考。当无法进行监考时，应部署可靠且有效的反作弊技术，并提供足够的警告。