How many participants do I need for qualitative research?

For those new to the qualitative research space, thereâs one question thatâs usually pretty tough to figure out, and thatâs the question of how many participants to include in a study. Regardless of whether itâs research as part of the discovery phase for a new product, or perhaps an in-depth canvas of the users of an existing service, researchers can often find it difficult to agree on the numbers. So is there an easy answer? Letâs find out.
Here, weâll look into the right number of participants for qualitative research studies. If you want to know about participants for quantitative research, read Nielsen Norman Groupâs article.
Getting the numbers right
So you need to run a series of user interviews or usability tests and arenât sure exactly how many people you should reach out to. It can be a tricky situation â especially for those without much experience. Do you test a small selection of 1 or 2 people to make the recruitment process easier? Or, do you go big and test with a series of 10 people over the course of a month? The answer lies somewhere in between.
Itâs often a good idea (for qualitative research methods like interviews and usability tests) to start with 5 participants and then scale up by a further 5 based on how complicated the subject matter is. You may also find it helpful to add additional participants if youâre new to user research or youâre working in a new area.
What youâre actually looking for here is whatâs known as saturation.
Understanding saturation
Whether itâs qualitative research as part of a masterâs thesis or as research for a new online dating app, saturation is the best metric you can use to identify when youâve hit the right number of participants.
In a nutshell, saturation is when youâve reached the point where adding further participants doesnât give you any further insights. Itâs true that you may still pick up on the occasional interesting detail, but all of your big revelations and learnings have come and gone. A good measure is to sit down after each session with a participant and analyze the number of new insights youâve noted down.
Interestingly, in a paper titled How Many Interviews Are Enough?, authors Greg Guest, Arwen Bunce and Laura Johnson noted that saturation usually occurs with around 12 participants in homogeneous groups (meaning people in the same role at an organization, for example). However, carrying out ethnographic research on a larger domain with a diverse set of participants will almost certainly require a larger sample.
Ensuring youâve hit the right number of participants
How do you know when youâve reached saturation point? You have to keep conducting interviews or usability tests until youâre no longer uncovering new insights or concepts.
While this may seem to run counter to the idea of just gathering as much data from as many people as possible, thereâs a strong case for focusing on a smaller group of participants. In The logic of small samples in interview-based, authors Mira Crouch and Heather McKenzie note that using fewer than 20 participants during a qualitative research study will result in better data. Why? With a smaller group, itâs easier for you (the researcher) to build strong close relationships with your participants, which in turn leads to more natural conversations and better data.
There’s also a school of thought that you should interview 5 or so people per persona. For example, if you’re working in a company that has well-defined personas, you might want to use those as a basis for your study, and then you would interview 5 people based on each persona. This maybe worth considering or particularly important when you have a product that has very distinct user groups (e.g. students and staff, teachers and parents etc).
How your domain affects sample size
The scope of the topic youâre researching will change the amount of information youâll need to gather before youâve hit the saturation point. Your topic is also commonly referred to as the domain.
If youâre working in quite a confined domain, for example, a single screen of a mobile app or a very specific scenario, youâll likely find interviews with 5 participants to be perfectly fine. Moving into more complicated domains, like the entire checkout process for an online shopping app, will push up your sample size.
As Mitchel Seaman notes: âExploring a big issue like young peoplesâ opinions about healthcare coverage, a broad emotional issue like postmarital sexuality, or a poorly-understood domain for your team like mobile device use in another country can drastically increase the number of interviews youâll want to conduct.â
In-person or remote
Does the location of your participants change the number you need for qualitative user research? Well, not really â but there are other factors to consider.
- Budget: If you choose to conduct remote interviews/usability tests, youâll likely find youâve got lower costs as you wonât need to travel to your participants or have them travel to you. This also affectsâŚ
- Participant access: Remote qualitative research can be a lifesaver when it comes to participant access. No longer are you confined to the people you have physical access to â instead you can reach out to anyone youâd like.
- Quality: On the other hand, remote research does have its downsides. For one, youâll likely find youâre not able to build the same kinds of relationships over the internet or phone as those in person, which in turn means you never quite get the same level of insights.
Is there value in outsourcing recruitment?
Recruitment is understandably an intensive logistical exercise with many moving parts. If youâve ever had to recruit people for a study before, youâll understand the need for long lead times (to ensure you have enough participants for the project) and the countless long email chains as you discuss suitable times.
Outsourcing your participant recruitment is just one way to lighten the logistical load during your research. Instead of having to go out and look for participants, you have them essentially delivered to you in the right number and with the right attributes.
Weâve got one such service at Optimal Workshop, which means itâs the perfect accompaniment if youâre also using our platform of UX tools. Read more about that here.
Wrap-up
So thatâs really most of what there is to know about participant recruitment in a qualitative research context. As we said at the start, while it can appear quite tricky to figure out exactly how many people you need to recruit, itâs actually not all that difficult in reality.
Overall, the number of participants you need for your qualitative research can depend on your project among other factors. Itâs important to keep saturation in mind, as well as the locale of participants. You also need to get the most you can out of whatâs available to you. Remember: Some research is better than none!