Fig. 6

Example of a natural experiment using observational data from a smartphone app for tracking activity. The Argus smartphone app (Azumio, Inc.), includes a social network that users can opt to join. Althoff and colleagues¹⁹ sought to uncover if and how forming social connections affects social activity. Since users who join and are active in the social network may be more intrinsically motivated to increase their activity, they used a natural experiment to isolate the effects of social influence from other factors that could influence activity. In particular, they compared the change in activity between a individuals who sent out a friend request (question mark) that was immediately accepted (check mark) and b individuals whose friend request was not accepted for more than 7 days. Note the curves in a and b are for illustrative purposes and do not represent actual subjects. Once a friendship is accepted, the user receives notifications of their connections’ activities (e.g., going for a run), and can comment on their connections’ activity posts (denoted by the heart, text box, and notification bell in a and b). Since the two groups were similar in all aspects except whether their friend request was accepted within 7 days, the additional increase in activity of the direct acceptance group can be attributed to social influence. c This social influence resulted in users taking 400 more steps per day on average. Error bars indicate bootstrapped 95% confidence intervals