How to justify sample size in qualitative research

Article

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.

By InterQ intern, Sakshi Shetty

Everyone wants to know the magical number for sample size when doing qualitative research.

Of course, when you’re doing quantitative research numbers matter more – especially when you’re aiming for statistically meaningful results. But when doing qualitative research, several factors must be considered before blindly accepting an arbitrary number. Here are some important points that should be kept in mind when thinking about sample size:

Point #1: Quality over Quantity

Whether your company is targeting moms from the Midwest with household incomes of $70k+, or teens who use Facebook more than 8 hours a week, or B2B decision makers in HR – you are most likely looking for insights on your services from a very specific audience type. That being said, the first objective when conducting qualitative market research should be to ensure the right people are recruited for the study.

The right respondents for the study are those who meet each and every criteria line-item identified from quantitative research studies, and also the criteria that the clients have identified through their own research. Thus, a high quality panel includes much more than just members who are pulled from a general population that falls within broad parameters. Only those participants who match the audience specifications and background relevance expressed by the client should be recruited.

Point #2: Choose an appropriate study design

The type of qualitative study is another important factor to consider when choosing sample size. There are various methods that can be used to gather insightful data, but not all methods may be applicable to your study and its aim. In-depth interviews, focus groups, and ethnographic research are the most common methods used in qualitative market research, each method being unique in the information it can provide and the setting it can be used in. Moreover, the types of questions being studied have an equally important role to play in deciding sample size. Thus before choosing a sample size, make sure all the parameters, aims, and controls are clearly outlined.

Point #3: Keep in mind the Principle of Saturation

A sample size should be large enough to sufficiently describe the phenomenon of interest, and address the research question at hand. But at the same time, a large sample size risks having repetitive data. The goal of qualitative research should thus be the attainment of saturation. Saturation occurs when adding more participants to the study does not result in obtaining additional perspectives or information. One can say there is a point of diminishing return with larger samples, as it leads to more data but doesn’t necessarily lead to more information.

The objective of qualitative research is to lessen discovery failure; whilst quantitative research aims to reduce estimation error. As qualitative research works to obtain diverse opinions from a sample size on a client’s product/service/project, saturated data does not serve to do anything. One respondent’s opinion is enough to generate a code, part of the analysis framework.

The goal of a qualitative study should be to have a large enough sample size to uncover a variety of opinions, but to limit the sample size at the point of saturation.

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

After bearing in mind all the factors mentioned above, there is a number you can aim for. Based on research conducted on this very issue, 30 seems to be a good number for the most comprehensive assessment. Some studies have noted having a sample size as little as 10 can be extremely fruitful, and still yield applicable results. This would of course be only after a rigorous recruiting process is put in place.

Our general recommendation for in-depth interviews is to have a sample size of 20-30, if we’re building similar segments within the population. In some cases, a minimum of 10 is acceptable – assuming the population integrity in recruiting.

If you would like to learn more about sample sizes and learn how to set up studies and perfect your moderating and interviewing skills, check out our InterQ Learning Labs training programs.

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