Echoes of the Ping: Indirect Effects of Mobile Notifications on

App Engagement

Businesses increasingly employ mobile notifications to increase app engagement. Firms typically evaluate notification effectiveness by measuring whether users click a notification and thereby visit the app, a pathway we call the direct effect. This paper examines whether firms systematically underestimate notification effectiveness because notifications increase app engagement even when users do not click them. Specifically, we examine an underexplored indirect effect, by which notifications create a memory trace of promoted content. When that content later becomes relevant, users recall it and open the app on their own, rather than by clicking the earlier notification. Because this indirect effect is difficult to isolate, we combine a field experiment comprising one million users of a customer-loyalty app with brick-and-mortar purchase data and a quasi-experimental shock from a mobile operating-system update. We find that the indirect effect is approximately twice as large as the direct effect and persists into the following day, well after the direct effect has faded. Importantly, the indirect effect is stronger for users encountering situational cues, such as making a purchase at a retailer featured in a prior notification, and occurs even after notifications were cleared from the device. These findings are theoretically relevant because they show that notifications shape app engagement not only through immediate attention but also through what users later recall from memory. They also inform notification policies, as we show that policies based on causal machine learning accounting for indirect effects are more effective than policies based on direct effects only.