Qualitative Sample Size Planner for Focus Groups and In-Depth Interviews
Plan how many focus groups or in-depth interviews you need across markets and segments, with recruits, over-recruitment, moderator days and saturation checks.
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How many focus groups or interviews do I need?
Qualitative sample size is decided by saturation: the point at which extra sessions stop producing new themes. It depends on how similar the participants are and how focused the topic is. Research gives useful anchors:
- Interviews: Guest, Bunce and Johnson (2006, Field Methods) found most themes emerged within 12 interviews in a fairly homogeneous group. Hennink and Kaiser's 2022 systematic review (Social Science & Medicine) found saturation at 9–17 interviews.
- Focus groups: Guest, Namey and McKenna (2017, Field Methods) found 80% of themes within 2–3 groups and 90% within 3–6. Hennink and Kaiser report 4–8 groups.
These numbers apply per segment. If users and non-users, or doctors in different countries, are expected to differ, each needs its own sessions.
How to use the qualitative sample planner
- Choose focus groups or in-depth interviews.
- Enter the number of markets, the segments in each and the sessions per segment.
- Set the over-recruitment rate, session length and how many sessions one moderator can run in a day.
- Read the total sessions, recruits, moderator days and the saturation check.
Over-recruitment and no-shows
Some recruited participants don't turn up. Over-recruiting by 20–25% for consumer groups is common, so 10 are recruited to seat 8. Professionals and physicians are harder to over-recruit because they expect to be paid even if not seated, so smaller over-recruits and back-up interviews are typical.
Worked example: a five-market physician study
A pharma team runs 45-minute interviews with three specialist types in five countries, 6 per specialty per country.
- 5 × 3 × 6 = 90 interviews
- 108 recruits with 20% over-recruitment
- At 5 interviews a day: 4 moderator days per market, 20 in total
Each specialty gets 30 interviews across markets, comfortably past the saturation range overall, though only 6 per country. Press Example to load it.
Frequently asked questions
How many people should be in a focus group?
Six to eight for consumers is standard. Mini-groups of four to six suit professionals, sensitive topics and online groups.
Are online focus groups different?
Online video groups usually seat 4–6 people and run for 60–90 minutes. Asynchronous online communities can involve 20–100 people over several days.
Can qualitative results be projected to the population?
No. Qualitative samples explain why and how. To measure how many, follow up with a survey and use the sample size calculator.
Need the respondents, not just the numbers?
Global Vox Populi runs quantitative and qualitative fieldwork in 170+ countries through its own proprietary panels of consumers, B2B and IT decision-makers, physicians, nurses, patients, caregivers and payers. ISO 9001, ISO 20252 and ISO/IEC 27001 certified and HIPAA compliant, following ESOMAR and Insights Association guidelines.
Check feasibilityLink to this tool
Free to use in proposals, courses and articles. If it helped, a link back is appreciated:
<a href="https://globalvoxpopuli.com/tools/focus-group-idi-planner/">Focus Group & IDI Sample Planner</a> by Global Vox Populi