Metrics question
Let's say that Facebook would like to change the user interface of the composer feature (the posting box) to be more like Instagram. Instead of a box, Facebook would add a "+" button at the bottom of the page. How would you test if this is a good idea?
- Meta
- Metrics
- Medium
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What this question tests
Experiment design skill, translating a UI hypothesis into a measurable test with the right metrics and guardrails.
How to approach it
- Restate the hypothesis: a plus-button entry point mimicking Instagram will increase post creation rate by feeling more familiar and inviting.
- Define the primary metric: post creation rate per active user, the direct behavior the change targets.
- Add secondary metrics: time to first post after opening the app, and post completion rate, to see if the new flow adds friction.
- Set guardrails: overall session length and any drop in comments or likes, in case the new entry point cannibalizes other engagement.
- Design the test: an A/B test with a representative sample, holding other variables constant, run long enough for significance.
- Define the decision rule upfront: ship if post creation rate improves without hurting guardrail metrics.
What a strong answer includes
- Distinguishes primary metric from guardrails, a core experiment design skill many candidates blur together.
- Adds post completion rate specifically, catching a subtle risk of higher intent but a worse completion funnel.
- Sets a clear ship decision rule before running the test, avoiding post-hoc rationalization of ambiguous results.
- Recognizes cannibalization risk, since a new entry point could reduce other feed engagement.
Common mistakes
- Measuring only post creation rate without any guardrail metrics.
- Not defining a ship decision rule before seeing results.
- Ignoring the risk that a new entry point could cannibalize existing engagement.
Likely follow-up questions
- How would you size the test to detect a meaningful effect confidently?
- What would you do if post creation rate rose but completion rate fell?
- How would you roll this out gradually if the test succeeds?
More metrics questions
- How would you measure the success of Facebook Likes?Meta · Metrics · Medium
- How would you measure improvements made to Facebook messenger?Meta · Metrics · Easy
- Imagine you are the PM in charge of Reactions on Facebook - the new way to interact with posts by using “love”, “haha”, “wow”, “sad”, and “angry” reactions. What would success look like in terms of number of non-like reactions per post at launch and how do you come up with this? Would this number differ by reaction? Why or why not?Meta · Metrics · Hard
- You launched a new signup flow to encourage new users to add more profile information. A/B test results indicate that the % of people that added more information increased by 8%. However, 7 day retention decreased by 2%. What do you do?Google · Metrics · Hard
- Define the metrics for YouTube search.Google · Metrics · Medium
- You are the PM of Instagram app. The MAU has been constant but DAU has declined. What will you do?Meta · Metrics · Medium
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Learn the skill behind it
Chapters of the AI PM course that teach what this question tests.
- Chapter 9: Prove it paid off: outcomes, economics, and pricing
- Chapter 2: Data fluency: SQL, logs, and reading the truth yourself
- Chapter 14: Get the job: the AI PM interview loop