The Evolution of IDIs

This article is an exploration of IDIs, in-depth interviews.

What is an IDI?

IDIs are a cornerstone of qualitative research.  QRCs have relied upon them for more than a half century to elicit information from consumers.  IDI’s can be referred to by several different names, all of which denote the same research technique:

  • individual interviews
  • in-depth interviews
  • individual depth interviews
  • individual face-to-face interviews

But what they all have in common is that they are conducted by one interviewer with one respondent. Typically IDI’s are:

  • Face-to-face, telephone, or online exchanges between a moderator and respondent
  • Interviews conducted in a research facility, at a respondent’s home or business (also called ethnographies or observational research), or on site (in situ) at a public location, (i.e., restaurant, bar, supermarket, auto dealer showroom, etc.)
  • With real-time communication
  • The sample size typically ranges from 12 to 60, depending on the study objectives and the number of various segments of the target population being analyzed
  • And, typically last from 30 to 60 minutes, occasionally stretching to 90 minutes (rare and expensive depending on the subject matter and context)

IDI’s are ideal for detailed exploration of specific ideas, or evaluation of concepts and materials that require thorough focus and concentration.  This mode of interviewing is very useful for executive interviews where participants may be reluctant to express their true feelings in a focus group, and for interviews to assess individual comprehension/attitudes toward a new concept.  IDI’s can also be the most appropriate technique for research covering more emotional topics, when the relationship between moderator and participant is essential to a successful outcome.

From In-Person to Telephone IDIs

The transition from in-person IDI’s to telephone IDI’s occurred fairly smoothly over time.  There has been widespread acceptance of the efficacy of telephone interviewing on the quantitative side for over fifty years; and telephone focus groups have been conducted and recognized for nearly that long.  A consensus similarly developed that telephone IDI’s are a valid technique for meeting a variety of research projects. 

But are IDI’s by phone as effective as those done face-to-face for all types of research projects?   An illustrative example--a client calls and says “we love what was accomplished for Nissan with laddering research, but we just can’t afford a bunch of IDI’s around the country.  We really want to do laddering.” [1]   Can laddering be done another (less expensive) way?”

Traditionally, laddering has been viewed as best conducted face-to-face where the moderator can get at the essence of a brand or product.  It works most effectively when a bond is created between the researcher and participant, with the researcher attuned to subtle shifts in the participant’s mood, as well as their willingness to continue in what can be a tedious process.   A skilled laddering interviewer gets to the depth of participant communication from successful face-to-face interactions by observing the emotionality behind the answers.  Trained and experienced researchers read the participant’s body language and use those signs to determine when to push, and when to pull back from the seemingly endless series of “why” questions. 

Testing the efficacy of laddering in IDI’s by telephone, approximately 60 in-depth phone interviews were conducted for an insurance company, exploring differences in motivation for purchasing several different insurance products.  The outcome verified the success of telephone laddering.  Effective questioning and probing, working off clues given by voice inflection, pauses between words and subjects, and other emotional auditory cues (e.g., nervous laughter, crying, etc.), yielded a similar level of useful data to that which could have been gathered from face to face laddering interviews.  The research effectively provided a road map for screening prospects and improving close rates when selling a variety of insurance products.

The Future of IDI’s:  Digital Data Collection?

Some qualitative researchers contend that IDI’s can be conducted online, via diaries, electronic bulletin boards, webcam interviews, etc.  However, at its core, it is crucial to conduct IDI’s with an individual in real time, without the distraction of the digital environment or the influence of other participants.  Using mobile devices for conducting IDI’s is seldom productive because respondents will be reluctant to participate long enough for the requirements of an in-depth interview.  Nor will they give the undivided attention necessary when on their smart-phones or tablets for thoughtful responses to a moderator.  Digital platforms provide opportunities for participants to share/post photos and videos of their environment or activity, but the time to probe will be limited by the length of time the participant is engaged in a two-way conversation with a researcher.  Webcam IDI’s, however, are becoming increasingly popular; they may be the next frontier in IDI’s and allow for successful incorporation of laddering techniques as well.

Still, each technique or methodology has its place.  It’s not about digital or in-person research; it’s about designing a research study using all the tools in the researcher’s tool box to get the best insights regardless of methodology.  In fact, telephone, digital, and in-person research each have different strengths that can be combined and leveraged to get better insights than either would provide alone.


Michele Zwillinger, PRC, is a founding member of the Qualitative Research Consultants Association (QRCA) and owner of Zwillinger Research  (  She specializes in new product research and developing proprietary techniques to maximize the benefits of traditional qualitative research.  Known for her expertise in laddering, Michele is a proponent of qualitative research that goes deep into consumer motivation to determine how needs, wants, values and lifestyle influence behavior. Ms. Zwillinger has been a member, committee chair, and presenter at the Qualitative Research Consultants Association for over 30 years, and was a presenter at the first QRCA Symposium on Excellence in Qualitative Research.

QRCA provides industry-leading resources that are essential to its members and the professionals who use qualitative research. As an association dedicated to advancing the discipline of qualitative research worldwide, QRCA’s nearly 1,000 global members apply their passion, creativity and experience to help clients tap into the power of qualitative marketing research.

 [1] Laddering is a qualitative research technique in which the interviewer repeatedly asks the respondent to take the last comment a little further, to get below the surface and uncover the core values of the participant, the category, the product or the brand.  This exercise serves to explain motivation, and ultimately, behavior. The laddering process starts with eliciting salient attributes, probing the importance of those attributes, moves on to consequences (often physical and psychological), and ends with identifying core values.  The laddering process can be used to understand brand personality, develop new products that are consistent with the consumer’s image of a brand, provide direction for advertising and marketing, and understand motivation/behavior to enhance the sales process.

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