Metrics question
A product manager decides to add threading to comments on group posts. We see comments per user increase by 10% but posts go down 2%. Why would that be?
- Meta
- Metrics
- Medium
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What this question tests
Tests diagnosing a metric divergence caused by a feature change, distinguishing engagement depth gains from a possible unintended side effect.
How to approach it
- State the puzzle plainly: threading increased comments per user but reduced posts, so engagement on existing posts rose while new content creation fell.
- Hypothesize a substitution effect: threading makes commenting on others' posts more satisfying and visible, so users spend their sharing energy replying instead of posting original content.
- Hypothesize a discovery effect: if threaded replies now surface more prominently in feed, original posts may get pushed down, discouraging posting since less content gets seen.
- Segment by user type, frequent posters versus frequent commenters, to see which group's behavior actually shifted.
- Check whether total time spent and total content consumed rose, since a shift toward richer conversation could still be a net positive even with fewer new posts.
What a strong answer includes
- Frames this correctly as substitution rather than a straightforward bug, since commenting and posting are alternative ways to express the same social energy.
- Proposes a plausible discovery-effect mechanism, threads crowding out original post visibility, not just a vague correlation.
- Weighs whether the net effect is actually positive, since deeper comment engagement isn't automatically worse than more original posts.
Common mistakes
- Treating the drop in posts as automatically bad without considering that deeper commenting might be a net positive.
- Not segmenting by user type to see who is actually posting less.
Likely follow-up questions
- Would you consider this a successful launch overall? Why or why not?
- How would you test the substitution hypothesis directly?
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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