Nudges are interventions promoting healthy behavior without forbidding options or significant incentives. As an example of a nudge, the Apple Watch encourages users to stand by delivering a notification if they have been sitting for the first 50 minutes of an hour.

Based on 76 billion minutes of observational standing data from 160,000 subjects in the public Apple Heart and Movement Study, amount of data in the field that makes this work one of the largest ever in the subject, we estimate the causal effect of this notification using a novel regression discontinuity design for time-series data with time-varying treatment. We show that the nudge increases the probability of standing by up to 44%, a very significant effect compared to what has been reported in the literature, remaining effective with time, even after almost 2 years. The nudge’s effectiveness increases with age, and it is independent of gender. Closing Apple Watch Activity Rings, a visualization of participants’ daily progress in Move, Exercise, and Stand, further increases the nudge’s impact. We conclude the presentation with some recent work on connections between geometry and causal inference.

The first part of the presentation is joint work with Achille Nazaret while the second is with Amir Farzam and Allen Tannenbaum.