In-depth Interviews Can Deliver Valid Market Research

Research from MIT and the University of Chicago suggests you can glean useful, reliable market research by conducting in-depth interviews with only a few customers.

Strength in small numbers

How many subjects should you interview for a reliable snapshot of your market? Although there’s no hard-and-fast rule, managers and researchers have determined that as few as 12 to 15 randomly-selected interview subjects can represent an entire segment accurately.1

Handful of interviews reveals nearly all unique customer needs2

In-depth Interviews Interviews 30 Customers

MIT and University of Chicago researchers interviewed 30 prospects for portable food carrying devices (coolers, picnic baskets, etc.). Seven analysts (some experts and some with minimal training) then coded the transcripts to identify specific customer needs and which customers revealed them first. The first 15 customers interviewed identified more than 90% of unique needs.

In-depth Interviews - Predictive Math Model

The researchers then developed a mathematical model based on the best-fit distribution to predict the percentage of customer needs a given number of one-hour interviews would reveal for a larger population. According to the model, it takes only 12 to 15 interviews to reveal nearly 80% of unique needs, regardless of the size of your market. Returns diminish quickly as the number of respondents increases.

Executive Summary

  • Researchers from MIT and the University of Chicago concluded that in-depth (±1 hour), individual interviews can provide reliable market research.
  • Although there’s no hard-and-fast rule, as few as 12 to 15 customer interviews can represent an entire market segment accurately.1
  • In-depth, individual interviews work well for identifying customer needs, understanding your product’s value and predicting marketplace behavior.1,3
  • Individual interviews may be more cost-effective than a comparable series of focus groups.2

The pros and cons of interviews

Numerous market research experts from the business world and academia have studied the benefits and limitations of interviews. Here are a few of their observations:

Pros / Cons Chart

Although interviews are not ideal for every research need, consider trying a few before moving to your next expansive (and expensive) study.


Helps you generate ideas and address problems you hadn’t considered before1

“Would a spill-proof container be an appealing feature?”

Reveals customer wants and needs effectively2

“Do customers really care about data security?”

Provides opportunity for interaction and nuanced responses1

A smaller sample allows more time with each participant and more flexibility to ask insightful follow-up questions that hadn’t been considered in advance.

Helps predict behavior1

“Will customers find enough value in this product to buy it?”

Defines and approximates product value3

“Why would customers buy this product, and how much would they pay?”

Enables precise sample control6

Lets you select specific participants—some who love your product, some who won’t buy it, and some who have never heard of it.

Prevents subjects from influencing each other’s responses4

Participants can’t intimidate or influence one another.

May be more cost-effective overall than focus groups2

Fewer total participants are required to reveal the same number of customer needs.

Short data collection period7

Get data in days or weeks, not months.


Limited ability to project trends4

“What will customers want 5 years from now?”

Not ideal for testing design appeal and/or ease of use1

“Do customers understand how to use this product?”

Requires more time per participant than other methods2

A typical individual interview should last about an hour compared to a two-hour focus group with six to eight participants.

No statistically valid data5

“How many customers prefer Brand A to Brand X?”

Unable to determine an ideal price point3

“Exactly how much should I charge?”

Introduces interviewer bias6

External factors such as the interviewer’s personal appearance can bias participants.

Eliminates group synergies2

Subjects can’t learn from one another or arrive at a consensus.

High cost per interview (requires a highly-skilled interviewer)2

Interviewer must be constantly ready to explore new lines of thinking instead of just reading from a prepared list of questions.

Complex transcription and analysis2

You might need to train several analysts.

1   Zaltman, G. How Customers Think: Essential Insights into the Mind of the Market. Boston, MA: Harvard Business School Press, 2003.

2   Hauser, J. and Griffin, A. The voice of the customer. Marketing Science Vol. 12 No. 1, Winter 1993.

3   McDonald, S. How to design and implement successful pricing research: counsel & caveats from the trenches. Professional Pricing Society Sixth Annual Pricing Conference, 1995.

4   U.S. Small Business Administration. Market research—types, methods & techniques. Online Women’s Business Center. Available: Accessed October 14, 2004.

5 Research Concepts, LLC. In-depth interviews. Available: Accessed May 23, 2005.

6  Informa Research Services. Condensed guide to market research. Available: Accessed May 23, 2005.

7  Oklahoma State University Bureau for Social Research. Study development and consultation. Available: Accessed March 23, 2005.

Caskey, B. (2001). Same Game New Rules (pp. 163-165). Carmel, IN: Winpointe Publishing.