One-on-one interviews are the most direct form of qualitative research. A researcher and a participant, with enough time to go deep. Done well, they surface the context, reasoning, and emotion behind a decision that no survey can capture.
This guide covers what qualitative interviewing is, when to use it, and how to get better results from in-depth interviews.
What Is Qualitative Interviewing?
Qualitative interviewing is a research method where a researcher conducts a structured or semi-structured conversation with a participant to explore their experiences, attitudes, and behaviors in depth.
Unlike a survey, where responses are constrained to predetermined options, an interview allows the researcher to follow threads, probe for detail, and surface meaning that wasn’t anticipated in the research design.
In market research, this is most commonly conducted as an in-depth interview (IDI) — a one-on-one session between a trained moderator and a single participant, typically lasting 45–60 minutes.
Types of Qualitative Interviews
Structured interviews follow a fixed set of questions in a fixed order. They’re easier to analyze across participants but less flexible — you get consistency at the cost of depth.
Semi-structured interviews use a guide of topic areas and suggested questions, but allow the moderator to follow unexpected directions. This is the standard format for most market research IDIs.
Unstructured interviews are more like guided conversations — the moderator has a topic, not a script. These work for exploratory research where you don’t yet know what questions to ask.
Most commercial qualitative research uses semi-structured IDIs: enough structure to compare across participants, enough flexibility to capture what you didn’t know to ask.
When to Use In-Depth Interviews
IDIs are the right tool when:
- The topic is personal or sensitive. Participants are more candid one-on-one than in a group.
- You need individual decision journeys. Purchase decisions, product adoption, switching behavior — these vary significantly by person and don’t surface well in group settings.
- You’re studying a niche audience. Experts, senior buyers, or hard-to-reach segments are easier to schedule individually.
- You want depth, not breadth. A focus group shows you what’s shared across a group. An IDI shows you what’s specific to an individual.
IDIs are not the right tool when you need to understand social dynamics, group norms, or how opinions form in reaction to other people — that’s a focus group job.
How to Conduct an In-Depth Interview
Write a discussion guide, not a script. Cover the key topic areas with suggested questions and probes. It’s a map — the moderator should follow the participant, not the page.
Start broad, then narrow. Open with context-setting questions that are easy to answer. Narrow into specific topics as the participant warms up. Save your most important probes for the middle of the session, once rapport is established.
Ask open-ended questions throughout. Every question should invite explanation, not a yes/no. “Tell me about the last time…” and “Walk me through how you…” are more productive than “Do you ever…”
Probe for specifics. The most useful material in any IDI usually comes from a follow-up, not the first answer. “Can you give me an example?” and “What happened next?” turn a general statement into usable evidence.
Manage time consciously. If you’re halfway through on time and barely into your guide, cut lower-priority topics — don’t rush the end. The last 10 minutes often produce the most candid answers.
Common In-Depth Interview Mistakes
Over-scripting. Reading questions verbatim kills rapport and causes you to miss natural openings to go deeper.
Asking leading questions. “Did you find the process frustrating?” is not a neutral question. “How did you find the process?” is.
Moving on too quickly. One probing follow-up often reveals more than the next five questions in your guide.
Ignoring contradictions. When a participant says something early that conflicts with something later, naming it gently often produces the richest material of the session.
FAQs
How many in-depth interviews do I need?
For a single segment, 8–12 IDIs typically reach saturation — the point where no new themes are emerging. For studies with multiple distinct segments, plan 8–10 per segment.
How long should an in-depth interview be?
45–60 minutes is the standard for most market research IDIs. 30 minutes is the minimum for anything substantive. Longer sessions (75–90 minutes) suit complex topics or ethnographic-style interviews.
Can in-depth interviews be conducted online?
Yes. Video IDIs are now standard practice and produce results comparable to in-person sessions for most topics. Remote formats also expand your reach to participants who couldn’t attend in person.
What’s the difference between an IDI and a user interview?
The terms are often used interchangeably. “User interview” typically appears in UX and product research; “IDI” is more common in market and consumer research. The method is the same.
How do I analyze in-depth interview data?
Thematic analysis is the standard approach — coding transcripts and identifying patterns across the full set. For a full breakdown of analysis methods, see our complete guide to qualitative research.
What to Remember
In-depth interviews are how you find out what people actually think, feel, and experience — the context behind the data that quantitative methods can’t reach.
The quality of an IDI depends almost entirely on the quality of the moderation: the guide, the questions, and the moderator’s ability to listen and follow the participant. Get those right, and IDIs are hard to beat for depth of understanding.
