

StreamHub, a video streaming app, noticed that users who enable push notifications appear to watch more content. The product manager wants to know whether notifications cause higher engagement or whether the relationship is driven by more engaged users being more likely to opt in.
Use the observational data below to distinguish correlation from causation. Quantify the naive relationship between notification opt-in and watch time, then assess whether the relationship remains after controlling for prior engagement.
| Segment | Notification Opt-In | Users | Avg Prior-Week Watch Hours | Avg Current-Week Watch Hours |
|---|---|---|---|---|
| High prior engagement | Yes | 800 | 12.0 | 13.2 |
| High prior engagement | No | 200 | 12.0 | 12.8 |
| Low prior engagement | Yes | 200 | 2.0 | 2.4 |
| Low prior engagement | No | 800 | 2.0 | 2.2 |
Assume the within-segment standard deviation of current-week watch hours is 4.0 hours for all four groups.
{"low_no_users":800,"high_no_users":200,"low_yes_users":200,"high_yes_users":800,"within_group_sd":4,"significance_level":0.05,"low_prior_watch_hours":2,"high_prior_watch_hours":12,"low_no_current_watch_hours":2.2,"high_no_current_watch_hours":12.8,"low_yes_current_watch_hours":2.4,"high_yes_current_watch_hours":13.2}Output(none)