Notifications increase engagement in the short term, and the effect decays — one estimate puts it at a factor of 0.993 per day over the first thirty days after download, which compounds substantially across a month. Notification frequency above what people expect or need produces fatigue and loss of interest.
How it was done
Micro-randomised trials of push notifications in behaviour-change apps, alongside Eysenbach’s analysis of attrition as the defining feature of eHealth deployments.
What it means
The decay is the planning assumption. Any product whose value depends on prompt volume is on a timer, and shipping more prompts to compensate accelerates the thing it is compensating for.
The attrition literature adds that long-term engagement comes from people recognising a concrete benefit, not from prompt volume. Low barriers to entry do not produce adherence, because the barrier to exit is just as low.
The way out is not more notifications but prompts carrying something a generic reminder app cannot: an actual remembered detail.