##### Scenario Partner-referral channel suddenly shows a sharp fall in first-time purchasers after a new splash pop-up asking visitors to download the mobile app was launched. ##### Question How would you investigate and confirm that the pop-up caused the drop in conversions from partner links? Assuming online traffic is unchanged, how would you quantify the trade-off between app-download uplift and lost first-purchase conversions? What metrics and experiment design would you propose to decide whether to keep, modify, or remove the pop-up? ##### Hints Map user funnel, build pre/post or A/B test, measure incremental value of app installs vs. lost orders, control for seasonality and partner mix.