In-depth interview questions: how to write a guide that actually works

Even highly skilled moderators struggle with a poorly designed discussion guide. Vague, leading, or incorrectly sequenced questions result in biased, polite, surface-level answers that offer very little analytical value.

To gather meaningful data, you need a deliberate framework for in-depth interview guide writing. This guide outlines how to structure a professional IDI discussion guide, breaks down the specific question types that yield genuine depth, and highlights critical mistakes that can unintentionally compromise your fieldwork.

(If you want to understand how to conduct an in-depth interview, read this blog)

Start by choosing the right Interview format & Sample size

Before writing a discussion guide, determine how much flexibility the conversation requires. This choice dictates which of the three primary interview formats you should use:

• Structured interview: These follow a rigid, identical sequence for every participant. They provide highly comparable data across a large sample but restrict the moderator from exploring unexpected, valuable insights.
  
  

•  Semi-structured interview: This format serves as the default for most applied research. It uses an established framework with core qualitative research questions and suggested probing questions, while allowing the interviewer to adapt the order and depth based on the live conversation.
  
  

• Unstructured interviews: These are purely conversational with minimal predetermined prompts. They are best reserved for highly exploratory research phases where you do not yet know enough about the topic to build a discussion guide.

For the vast majority of market research interview questions and B2B interview questions, a semi-structured approach offers the ideal balance of consistency and depth. Another decision that teams establishing their methodology or defining what is qualitative research often deliberate is Sample size. The standard IDI sample size is best identified by deciding how many ‘cells’ you want to analyse your dataset by. 

For instance, various combinations of 2 variables (age & gender) would amount to 4 ‘cells’ to analyse data by. Let’s say you want to analyse each of these cells and understand how the findings differ between these 4 cells. In that case, 5-10 interviews per cell would suffice for most research studies. Another way that researchers decide on sample size is by saturation – they estimate a point in fieldwork where consecutive new interviews are likely to stop revealing new themes, behaviours or issues.

How to structure an IDI discussion guide

A well-constructed, in-depth interview guide flows through four distinct phases. Maintaining this logical sequence ensures the participant remains engaged and comfortable.

1. Warm-up: building calibration

Start with low-stakes, easy-to-answer questions to help the participant settle in. Use simple introductory prompts:

• "Tell me a bit about your role and your day-to-day responsibilities."

• "What does a typical week look like for you?"

These questions allow you to gauge how the participant communicates, how comfortably they handle open-ended prompts, and how much prompting they might need later.

2. Broad exploration: establishing context

Allow the participant to define the topic area in their own words before introducing your specific research constraints. This phase often surfaces organic priorities and terminology you might not have anticipated.

• "Walk me through your current process for [the relevant task or decision]."

• "What comes to mind when you think about [the category or topic]?"

3. Covering specific information areas: addressing core objectives

This section houses the bulk of your qualitative interview questions, organised directly around your primary research targets. Mix different question types to gather well-rounded data:

• Descriptive questions capture step-by-step actions: "What did you do right after you noticed that error?"

• Comparative questions reveal decision logic: "How does this option compare to the system you used previously?"

• Causal questions uncover underlying motivations: "What led you to make that change at that specific time – not earlier, nor later?"

• Hypothetical questions help explore alternative scenarios or sensitive topics: "If you could change one thing about this implementation process, what would it be?"

4. Wrap-up: closing the session

Conclude by giving the participant space to share any thoughts that your structured prompts might have missed:

• "Is there anything about this topic that we haven't covered that you think is important?"

• "If you were running this project, what would you want to make sure we fully understood?"

What makes a question work in an in-depth interview

Effective in-depth interview questions live up to three core characteristics: they are open-ended, anchored in specificity, and entirely neutral.

• Open-ended framing: Avoid questions that invite simple, one-word responses. For example, instead of asking, "Did you compare other options before choosing this product?", use: "Walk me through how you decided between the options you were considering." The latter invites a narrative that might uncover more data, rather than a simple "Yes” or "No" response.
  
  

• Anchored in specificity: Focus your prompts on real, recent moments rather than generalised behaviours. Asking, "How do you feel about customer service in general?" could be a great open-ended start to exploring the customer service experience. However, following it up with a prompt helps uncover more: "Tell me about the last time you contacted customer support, from the moment the issue started to how it was resolved."
  
  

• Neutrality: Keep your own assumptions out of the prompt. A question like, "What frustrates you most about this software?" assumes frustration exists. A neutral alternative is: "How would you describe your experience with this software – what works, what does not?"

The art of probing

The questions on the page provide the framework, but the true depth of qualitative research is achieved during follow-up questions. Initial responses from participants are often surface-level. Effective moderators use targeted probes to uncover deeper details, while sticking strictly to the participant's own language.

Built-in reminders to include in your guide:

• "Can you tell me a little more about that?"

• "What do you mean by [specific word the participant just used]?"

• "What was going through your mind at that exact moment?"

•  “What would people like you (Projection) feel about this?”

Avoid paraphrasing their answers into industry jargon or your own research terms. The moment you reframe their response, you risk leading them toward agreeing with your interpretation rather than expanding on their own. If you plan to host your project transcripts and media on a qualitative research platform, keeping these responses unguided and authentic ensures much higher data quality during final analysis.

Here are some probing mistakes that could yield low-quality data from IDIs:

• Double-barrelled questions: Asking two things at once ("What did you like about the platform, and would you recommend the platform?") forces the participant to choose the easier half to answer, causing the other half to be lost. Split these into separate points, i.e. “All things considered, would you recommend the platform?" and “Is there anything you liked about the platform – can you tell me more about this?”
  
  

• Leading questions: Prompts like "Don't you think the new layout is more intuitive?" signal the expected answer. Reframe neutrally: "What is your reaction to the new layout?"
  
  

• Over-relying on "Why": Direct "why" questions can inadvertently sound accusatory, causing participants to over-rationalise their habits or become defensive. Use softer entry points like "What led you to that decision?"
  
  

• Re-asking screener data: Do not waste valuable interview time on probes that simply confirm details that your recruitment screening process has already verified.
  
  

•  Rigid guide execution: Treat your guide as a flexible framework. If a participant naturally opens a thread that connects to a core objective early in the conversation, follow it immediately rather than forcing them to wait for a specific section.

An adaptable IDI discussion guide template

Use this streamlined structure as a foundation for your consumer or B2B qualitative studies:

• Introduction (5 min): Introduce self, explain the interview purpose, secure recording consent, and set duration-related expectations.
  
  

• Warm-up (5 to 10 min): Casual, low-stakes background questions related to the user's environment.
  
  

• Broad Exploration (15 to 20 min): Open-ended prompts to understand how the participant frames the category organically.
  
  

• Core Research Questions (30 to 40 min): Descriptive questions, comparative questions, and causal questions organised by project objectives.
  
  

• Projective/Hypothetical (5 to 10 min): Creative or alternative scenario prompts & techniques to surface deeper distinctions.
  
  

• Wrap-up (5 min): Open floor for final participant thoughts and next steps.

As a skilled moderator, treat a template as a living document. After the first two or three interviews, review your guide to sharpen questions that felt clunky, remove unproductive probes, or add new angles surfaced by early participants.

FAQs

What makes a good in-depth interview question?

It is open-ended, could be focused on a specific real-world event, and is entirely free of the interviewer's assumptions or expected answers.

What is the difference between structured and semi-structured interview questions?

Structured questions follow a rigid, unchangeable sequence for every participant to maximise comparability. Semi-structured questions use a flexible framework that allows the interviewer to probe and alter the order based on the flow of conversation.

How do I write an IDI discussion guide?

Organise the guide into four sequential phases: a low-stakes warm-up, a broad exploration of the topic, focused probing tailored to your core objectives, and an open-ended wrap-up.

How many in-depth interviews should I conduct?

Most studies target an IDI sample size of 10 to 30 interviews per segment, concluding fieldwork when you hit saturation, the point where new interviews no longer yield fresh insights.

What is a good probing question in qualitative interviews?

Effective probes build directly on the participant’s exact words. Examples include: "Can you say more about that?" or "What did you mean by [the word they used]?"

Why do "why" questions sometimes produce weaker answers?

They can make participants feel put on the spot or defensive, leading them to rationalise behaviours after the fact. Replacing "why" with "What led to that?" or "What was going through your mind?" yields more authentic responses.