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Data Saturation Qual Research

Article Summary: Data saturation is a principle in qualitative research whereby you can have significantly smaller sample sizes than in quantitative research. This is because of “data saturation” which means you start to hear the same themes repeatedly in a research interview.

Whether you’re in academia or in business, and working in qualitative research, you may have come across or be familiar with the term “saturation” in qualitative research. It’s an important principle, and actually one of the defining characteristics of qualitative research – since qualitative research deals with small sample sizes – so we want to dedicate a post to saturation in qualitative research.

First, let’s discuss sample sizes in qualitative research

Before we dive into saturation in qualitative research, we first need to define qualitative research, and specifically, discuss sample sizes in qualitative research. Unlike quantitative research, which is rooted in statistical analysis and seeks to analyze “how many” or patterns in data, qualitative research focuses on themes. Qualitative data is collected through interviewing, observation, and sometimes task completion. The most common methodologies used in market and UX research are in-depth interviews, focus groups, ideation groups, dyads, triads, ethnographies, and social listening studies.

A key component of qualitative research is smaller sample sizes that are homogenous in nature. This means that instead of interviewing a population with a wide-array of characteristics, qualitative research first focuses on segmenting audiences into similar psychographic qualities (often called “personas.”) This ensures that the research study is aimed at exploring themes or ideas from a specific subset of a population. For example, a segment might be “small business owners who use Brand X to order supplies for their business.” The idea is to ensure that the segments have well-defined characteristics, which are screened during the recruiting process.

Since there will be highly defined segments, qualitative researchers focus on speaking to a defined number of participants in order to explore themes.

How many participants should a qualitative study have?

We’ve written on this topic of sample sizes before, so we won’t spend this post on that, but typically (again, for homogenous populations), between 10-20 total participants, per segment, is a solid number. Really, what will be the cutoff is when you hit saturation in your research, so let’s focus on what saturation is.

Saturation in qualitative research is when, through the course of interviewing (or observation), you notice the same themes coming out, repeatedly. As you interview more and more participants, you stop finding new themes, ideas, opinions, or patterns. Essentially, saturation is when you get diminishing return, despite talking to more and more people.

How soon will you hit saturation? That depends, of course. For highly homogenous samples (very niche industries/job roles) for examples, saturation can happen after as little as 5 interviews. If you have a more diverse population sample (teenagers who use a particular social media app for 20+ hours a week, for example), you may need to interview 30 or more people before you hit saturation of themes.

Saturation can also depend on the specificity of the study. For example, if you are doing a UX study and asking people to test out an app, you may find pretty quickly (after maybe 4-5 interviews) that everyone is having the same reaction or moving through the product in the same way. You’re studying a specific task with defined variables, so saturation is likely to happen sooner.

However, if you are running an ideation workshop, testing reactions to advertising, or studying complex products, saturation will take longer: you may need to talk to 20+ participants before you see those patterns become really defined and you feel you’ve reached saturation, by exploring all of the available themes.

Saturation is extremely important – pay attention to it

If you find that you’ve reached saturation very quickly, don’t necessarily cut the study short right away. First ask: Have we thoroughly covered the audience for this idea/product? If not, recruit additional participants who fit your segment, and test their ideas. Conversely, if you’ve spoken to 45 people and have not heard anything new in the previous 10 interviews, likely you won’t be uncovering too many new themes, so it may be wise to stop at the number you’re currently at.

There are other variables involved in saturation, such as the quality of your recruiting, how you ask your questions (your discussion guide), and the overall focus of your objectives. We will cover those in subsequent posts. For now, we hope you have an understanding of what saturation is and why it’s so critical in qualitative research.

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Author Bio: Joanna Jones is the founder and CEO of InterQ Research. At InterQ, she oversees study design, manages clients, and moderators studies.