In-depth interviews, commonly known as IDIs, are one of the most powerful qualitative research methods used to uncover rich, detailed insights directly from participants. While surveys and quantitative research provide the “what,” IDIs help understand the “why” behind consumer attitudes, motivations, and behaviors.
This guide offers a simple and practical overview of what IDIs are, how they work, and why organisations use them.
What Are In-Depth Interviews (IDIs)?
An In-Depth Interview is a one-on-one conversation between a trained interviewer (moderator) and a respondent. Unlike structured surveys, IDIs are conversational, flexible, and designed to explore thoughts, perceptions, beliefs, and experiences in detail.
The purpose of an IDI is to understand personal viewpoints, not just collect short answers. This allows researchers to dig deeper into the reasoning behind opinions and behaviors.
How IDIs Work
IDIs can be conducted in-person, over the phone, or through video platforms such as Zoom or Teams. The process typically involves:
- Preparing a discussion guide with key topics and open-ended questions
- Conducting a one-on-one interview lasting 30–60 minutes
- Encouraging respondents to speak freely while the moderator probes for clarity and depth
- Recording and transcribing interviews for analysis
- Identifying themes, patterns, and insights across interviews
IDIs are semi-structured, meaning moderators follow a guide but adapt questions based on the flow of conversation.
Why IDIs Are Valuable in Market Research?
IDIs provide something that other methods often cannot — depth. Researchers use IDIs when they need context, emotions, or personal experiences that shape decision-making.
Key advantages include:
- Rich, Detailed Insights:
IDIs capture tone, emotions, and stories, revealing reasoning behind attitudes. - Flexibility to Probe and Explore:
Moderators can ask follow-up questions to clarify or go deeper into any topic that emerges during the conversation. - Ideal for Complex or Sensitive Topics:
Some subjects are better discussed privately than in a group setting or survey. - Better Understanding of Customer Journeys:
IDIs help map experiences, challenges, and expectations across stages of interaction with a brand or product.
When Should You Use IDIs?
IDIs are useful when you want to explore thoughts, motivations, and behaviors in depth. They are commonly used for:
- New product or concept exploration
- Customer experience or journey mapping
- Brand perception and positioning research
- Understanding unmet needs or pain points
- Sensitive topics where privacy matters
- B2B research with niche or high-expertise audiences
IDIs work well at the exploratory stage of research, especially before large-scale surveys.
IDIs vs. Focus Groups: What’s the Difference?
Both IDIs and focus groups are qualitative methods, but they serve different purposes.
| Aspect | IDIs (One-on-One) | Focus Groups (Group Discussion) |
| Participants | 1 at a time | 6–8 per session |
| Environment | Private | Group setting |
| Depth | High, personal | Breadth of views |
| Best For | Sensitive or detailed topics | Group dynamics and idea testing |
IDIs are more personal and confidential, making them ideal for exploring individual experiences. Focus groups, on the other hand, highlight collective opinions and group reactions.
Limitations of IDIs
While IDIs offer strong value, they do require time and expertise. Common limitations include:
- Smaller sample size, so results are not statistically generalizable
- Skilled moderators are required for effective probing
- Time-consuming scheduling and analysis
For this reason, IDIs are often paired with quantitative research for a balanced view.
How Many IDIs Are Enough?
Most projects include 8 to 20 IDIs, depending on the audience, objectives, and complexity. The aim is to reach “insight saturation”, the point at which new interviews no longer reveal new themes.
In-depth interviews are a powerful tool for understanding people beyond surface-level responses. They provide context, emotion, and personal experience the type of insight that shapes meaningful strategies. IDIs help businesses, brands, and researchers move beyond numbers to uncover the motivations and human stories that influence decisions.
For companies conducting market research, IDIs often serve as a foundation for deeper understanding which can later be validated through quantitative methods.