Product design question

How would you design a test to measure the success of using a gift card promotion to get Prime members to download the Prime mobile app?

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What this question tests

Experiment design skill: defining a valid test for a specific marketing-driven adoption goal.

Clarify the goal: measure whether a gift card promotion causes Prime members to download and use the mobile app, not just claim the gift card.
Design the test: randomly assign eligible Prime members to a treatment group (offered the gift card for downloading) and a control group (no offer).
Define the primary metric: app download and first-session completion rate, comparing treatment versus control.
Define a downstream metric: app retention and usage 30 days later, since a one-time download driven by incentive may not translate to habitual use.
Control for confounds: ensure both groups are similar in demographics and prior engagement, and run the test long enough to capture meaningful behavior.
Define success criteria: a statistically significant lift in download rate and sustained 30-day retention above a set threshold.

Designs a proper randomized control test rather than just measuring downloads after a broad promotion.
Explicitly separates short-term download lift from sustained 30-day retention, avoiding a metric that rewards one-time incentive-chasing.
Gives an illustrative threshold, e.g. requiring 25% 30-day retention among incentivized downloaders to call the test successful, marked as an assumption.
Addresses cost: comparing gift card cost per incremental retained user against typical acquisition cost benchmarks.

Measuring only download count without checking if the incentive attracted low-intent, one-time users.
Not proposing a control group, making it impossible to isolate the promotion's real causal effect.

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