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Article Summary: A common question in qualitative research is the ideal number of participants that should be in a study. The number depends on various factors including how participants are segmented, the study design that’s being used, and the principle of data saturation.

If we were to assemble a list of “most asked questions” that we receive from new clients, it’s this:

What is the ideal sample size in qualitative research?

It’s a great question. A fantastic one. Because panel size does matter, though perhaps not as much as it does in quantitative research, when we’re aiming for a statistically meaningful number. Let’s explore this whole issue of panel size and what you should be looking for from participant panels when conducing qualitative research.

First off, look at quality versus quantity

Most likely, your company is looking for market research on a very specific audience type. B2B decision makers in human resources. Moms who live in the Midwest and have household incomes of $70k +. Teens who use Facebook more than 8 hours a week.

Specificity is great thing, and without fail, every client we work with has a good grasp on their audience type. In qualitative panels, therefore, our first objective is to ensure that we’re recruiting people who meet each and every criteria line-item that we identify through quantitative research  – and the criteria that our clients have pinpointed through their own research. Panel quality – having the right members in the panel – is so much more important than just pulling from a general population that falls within broad parameters. So first and foremost, we focus on recruiting the right respondents who match our audience specifications.

Study design in qualitative research

The type of qualitative study chosen is also one of the most important factors to consider when choosing sample size. In-depth interviews, focus groups, and ethnographic research are the most common methods used in qualitative market research, and the types of questions being studied have an equally important factor as the sample size chosen for these various methods. One of the most important principles to keep in mind – in all of these study designs – is the principle of saturation.

The objective of qualitative research (as compared to quantitative research) is to lessen discovery failure; in quantitative research, the objective is to reduce estimation error. Here’s where the principle of saturation comes in: With saturation, we say that the collection of new data isn’t giving the researcher any new additional insights into the issue being investigated. Qualitative seeks to uncover diverse opinions from the sample size, and one person’s opinion is enough to generate a code (part of the analysis framework). There is a point of diminishing return with larger samples; more data does not necessarily lead to more information – it simply leads to the same information being repeated (saturation).

The goal, therefore, is to have a large enough sample size in a qualitative study that we’re able to uncover a range of opinions, but to cut the sample size off at the number where we’re getting saturation and repetitive data.

So … is there a magical number to aim for in qualitative research?

So now we’re back to our original question:

What is the ideal sample size in qualitative research?

We’ll answer it this time. Based on studies that have been done in academia on this very issue, 30 seems to be an ideal sample size for the most comprehensive view, but studies can have as little as 10 total participants and still yield extremely fruitful, and applicable, results. (This goes back to excellence in recruiting.)

Our general recommendation for in-depth interviews is a sample size of 30, if we’re building a study that includes similar segments within the population. A minimum size can be 10 – but again, this assumes the population integrity in recruiting.

Let’s discuss your project and the type of sample size that would work best. Request a proposal >

Author BioTamara Irminger Underwood is the Head of Qualitative research at InterQ Research. She moderates interviews and helps write reports.