On the Causal Effect of Badges

Tomasz Kusmierczyk, Manuel Gomez-Rodriguez

Abstract: A wide variety of online platforms use digital badges to encourage users to take certain types of desirable actions. However, despite their growing popularity, their causal effect on users» behavior is not well understood. This is partly due to the lack of counterfactual data and the myriad of complex factors that influence users» behavior over time. As a consequence, their design and deployment lacks general principles. In this paper, we focus on first-time badges, which are awarded after a user takes a particular type of action for the first time, and study their causal effect by harnessing the delayed introduction of several badges in a popular Q&A website. In doing so, we introduce a novel causal inference framework for first-time badges whose main technical innovations are a robust survival-based hypothesis testing procedure, which controls for the heterogeneity in the benefit users obtain from taking an action, and a bootstrap difference-in-differences method, which controls for the random fluctuations in users» behavior over time. Our results suggest that first-time badges steer users» behavior if the initial benefit a user obtains from taking the corresponding action is sufficiently low, otherwise, we do not find significant effects. Moreover, for badges that successfully steered user behavior, we perform a counterfactual analysis and show that they significantly improved the functioning of the site at a community level.