Five interviews will uncover about 80% of usability issues in a single user segment. For broader product decisions (new features, market entry, pricing), aim for 12-15 interviews across 2-3 segments. The key is not a magic number but reaching saturation: the point where new interviews stop revealing new insights.
Interview Counts by Decision Type
| Decision Type | Recommended Interviews | Why |
|---|---|---|
| Usability testing | 5 per segment | Nielsen's research shows 5 users find 85% of issues |
| Feature validation | 8-12 | Enough to see patterns across different use cases |
| New product/market | 15-20 | Broader segments require more data points |
| Pricing research | 10-15 | Price sensitivity varies widely, need more coverage |
| Persona development | 12-15 per persona | Saturation typically hits around interview 12 |
How to Know You Have Reached Saturation
Track themes across interviews. After each conversation, write down the top 3 insights. When you start hearing the same themes repeated for 3 consecutive interviews without new information, you have reached saturation for that segment.
A practical approach:
- Conduct 5 interviews
- Synthesize findings and identify themes
- Check if any theme appeared in only 1 interview (potential outlier) or in 4+ (strong signal)
- If you have uncertain themes, conduct 3-5 more targeted interviews
- Stop when new interviews confirm existing findings without adding new ones
The discovery guide covers the full process from research planning through synthesis.
Quality Over Quantity
Ten poorly conducted interviews are less valuable than three well-conducted ones. Each interview should have:
- A clear research question (what are you trying to learn?)
- Open-ended questions that do not lead the participant
- Silence after questions (let the participant think and elaborate)
- Follow-up probes on interesting answers ("Tell me more about that")
The biggest mistake PMs make is asking "Would you use this feature?" instead of "Tell me about the last time you experienced this problem." The first question gets wishful thinking. The second gets real behavior.
Segment Matters More Than Count
Five interviews with your ideal customer profile are more valuable than 20 interviews with mixed segments. Before scheduling interviews, define:
- Who is your target user (role, company size, industry)?
- What specific behavior or problem are you studying?
- What would change your decision based on what you learn?
Use the user persona builder to define your segments before recruiting participants. The JTBD builder helps you frame the jobs-to-be-done you are investigating.
When to Skip Interviews Entirely
Not every decision needs interviews. Skip them when:
- You have strong quantitative data (analytics, A/B test results) that answers the question
- The change is easily reversible and you can ship-and-measure instead
- You have talked to this segment recently (within 4-6 weeks) about a related topic
- The decision is driven by technical or business constraints, not user preference
The A/B test calculator helps you determine whether quantitative testing is sufficient for your decision.