Massive Open Online Courses (MOOCs) have the potential to democratize education by improving access. Although retention and completion rates for non-paying users have not been promising, these statistics are much brighter for users who pay to receive a certificate upon completing the course. We investigate whether paying for the certificate option can increase engagement with course content. In particular, we consider two such effects: (a) the certificate effect, which is the boost in motivation to stay engaged in order to receive the certificate; and (b) the sunk-cost effect, which arises solely because the user paid for the course. We use data from over 70 courses offered on the Coursera platform and study the engagement of individual participants at different milestones within each course. The panel nature of the data enables us to include controls for intrinsic differences between non-paying and paying users in terms of their desire to stay engaged. We find evidence that the certificate and sunk-cost effects increase user engagement by approximately 8%-9%, and 17%-20%, respectively. However, whereas the sunk-cost effect is transient and lasts only for a few weeks after payment, the certificate effect lasts until the participant reaches the grade required to be eligible to receive the certificate. We discuss the implications of our findings for how platforms and content creators may want to design course milestones and schedule the payment of course fees. Given that greater engagement tends to improve learning outcomes, our study serves as an important first step in understanding the role of prices and payment in enabling MOOCs to realize their full potential.

大规模的在线公开课程（MOOC）具有通过提高普及率使教育民主化的潜力。尽管非付费用户的保留率和完成率并不令人满意，但是对于付费完成课程后付费获得证书的用户而言，这些统计数据要亮得多。我们调查支付证书选项是否可以增加对课程内容的参与度。特别是，我们考虑了两个这样的影响：（a）证书效应，这是为了获得证书而保持参与的动机的增强；（b）沉没成本效应，仅由于用户为课程付费而产生。我们使用Coursera平台上提供的70多个课程的数据，并研究每个课程中各个里程碑的参与者的参与度。数据的面板性质使我们能够包括控制非付费用户和付费用户之间保持联系意愿的内在差异的控件。我们发现有证据表明，证书和沉没成本效应分别使用户参与度提高了大约8％-9％和17％-20％。但是，尽管沉没成本效应是短暂的，并且仅在付款后持续数周，但证书效应一直持续到参与者达到有资格获得证书所需的等级为止。我们讨论了研究结果对平台和内容创建者可能如何设计课程里程碑并安排课程费用支付的意义。鉴于更多的参与往往会改善学习成果，