In-Depth Interview Method
Semi-Structured and Unstructured In-Depth Interviewing · Also known as: IDI, qualitative interview, one-on-one interview, in-depth interviewing
In-depth interviews are a qualitative research method in which a trained interviewer conducts one-on-one conversations with individual participants using open-ended questions to explore their experiences, perspectives, and understandings of a phenomenon. Developed in the 1950s by Rogers and Hyman, the method varies along a spectrum from structured (standardized question sets) to semi-structured (guided topic areas with flexibility) to unstructured (emergent, conversational). In-depth interviews are widely used in sociology, psychology, health sciences, anthropology, and organizational research to capture rich, detailed narratives and personal meaning.
Read the full method
Sign in with a free account to read this section.
Method map
The neighbourhood of related methods — select a node to explore.
When to use it
In-depth interviews are most valuable when exploring sensitive or personal topics (grief, trauma, marginalized identities, moral dilemmas); understanding individual agency, meaning-making, and narrative identity; investigating rare or hard-to-reach populations; exploring complex decisions or life transitions; conducting biographical or narrative research; or validating and contextualizing findings from surveys or focus groups. They are less suitable when seeking consensus views (focus groups better), when precise measurement of population-level variables is the goal, or when participants are unable to articulate their experiences (very young children, severe cognitive impairment).
Strengths & limitations
- Captures rich, detailed narratives and personal meaning; allows exploration of complexity, contradiction, and nuance within individual experience.
- Psychological safety and privacy enable disclosure of sensitive information that participants might withhold in groups.
- Flexibility to pursue emergent themes and unexpected insights; interviewer can adapt questions and probes in real time.
- Excellent for exploring causation and agency—how participants explain their own motivations and outcomes.
- Suitable for diverse populations and rare experiences; purposive sampling allows recruitment of strategically informative cases.
- Time-intensive in both data collection and analysis; transcription and coding of 20 interviews can require 100+ hours.
- Small sample sizes (typically 12–30) limit statistical representativeness; findings are exploratory and context-specific.
- Interviewer bias and subjectivity; interviewer's assumptions, tone, and follow-up choices shape what participants reveal.
- Social desirability bias; participants may present idealized or socially acceptable versions of themselves.
- Difficulty generalizing from individual cases; findings apply to participants' contexts, not necessarily to broader populations.
Frequently asked
How many interviews do I need?
Saturation (no new themes emerging) typically occurs at 12–20 interviews for homogeneous populations with a narrow research question. For heterogeneous populations or broader topics, 20–30+ interviews may be needed. Aim to conduct interviews until no substantially new themes appear in the last 3–5 interviews. Quality matters more than quantity; a few very detailed, rich interviews may yield more insight than many superficial ones.
Should I use a semi-structured or unstructured interview guide?
Semi-structured is most common: a guide with topic areas and open-ended prompts ensures consistency across interviews while allowing flexibility. Unstructured (conversational, no guide) works for exploratory research where topics emerge from participants. Fully structured (identical questions) sacrifices depth for consistency, useful mainly for comparative analysis. Start semi-structured unless your research is explicitly exploratory or your participants are very homogeneous.
How do I minimize interviewer bias?
Use reflexivity: document your assumptions, positionality (identity, relationship to topic), and how these may influence interpretation. Use consistent interview technique across participants (same opening, similar question order). Avoid leading questions or over-interpreting ambiguous responses. Use debriefing or peer review: discuss interpretation with co-researchers. Consider member checking: share preliminary findings with participants to verify accuracy.
Can I conduct interviews via phone or video instead of in-person?
Yes. Phone interviews reduce cost and geographic barriers but may limit rapport and non-verbal observation. Video (Zoom, Skype) preserves some non-verbal cues. Document the medium used and discuss any differences in data quality or participant engagement. Some sensitive topics may require in-person interviewing for safety and psychological comfort.
How do I handle emotional disclosure or distress in interviews?
Anticipate sensitive topics and prepare: have support resources available (mental health referrals, crisis hotlines). Use trauma-informed interviewing: slow pacing, explicit permission to pause or stop, checking in. Debrief after interviews to process emotional impact on both participant and interviewer. Consider whether the research question requires depth on painful experiences or whether surface-level understanding is sufficient. Ethics approval should address duty of care and limits to confidentiality.
Sources
- Kvale, S. (1996). InterViews: An Introduction to Qualitative Research Interviewing. SAGE Publications. ISBN: 978-0761908631
- Patton, M. Q. (2002). Qualitative Research and Evaluation Methods (3rd ed.). SAGE Publications. ISBN: 978-0761919676
- Bernard, H. R. (2006). Research Methods in Anthropology: Qualitative and Quantitative Approaches (4th ed.). Rowman & Littlefield Publishers. ISBN: 978-0742539136
- Rubin, H. J., & Rubin, I. S. (2005). Qualitative Interviewing: The Art of Hearing Data (2nd ed.). SAGE Publications. ISBN: 978-0761928479
How to cite this page
ScholarGate. (2026, June 4). Semi-Structured and Unstructured In-Depth Interviewing. ScholarGate. https://scholargate.app/en/qualitative-research/in-depth-interview-method
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
- Focus Group MethodologyQualitative Research↔ compare
- Member Checking and Respondent ValidationQualitative Research↔ compare
- Participant ObservationQualitative Research↔ compare
- Qualitative Evidence Synthesis MethodsQualitative Research↔ compare
- Reflexivity in Qualitative ResearchQualitative Research↔ compare