August 8, 2019
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How many participants do I need for qualitative research?

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For those new to the qualitative research space, there’s one question that’s usually pretty tough to figure out, and that’s the question of how many participants to include in a study. Regardless of whether it’s 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? Let’s find out.

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Here, we’ll look into the right number of participants for qualitative research studies. If you want to know about participants for quantitative research, read Nielsen Norman Group’s article.

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Getting the numbers right

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So you need to run a series of user interviews or usability tests and aren’t sure exactly how many people you should reach out to. It can be a tricky situation – 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.

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It’s 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 you’re new to user research or you’re working in a new area.

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What you’re actually looking for here is what’s known as saturation.

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Understanding saturation

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Whether it’s qualitative research as part of a master’s thesis or as research for a new online dating app, saturation is the best metric you can use to identify when you’ve hit the right number of participants.

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In a nutshell, saturation is when you’ve reached the point where adding further participants doesn’t give you any further insights. It’s 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 you’ve noted down.

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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.

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Ensuring you’ve hit the right number of participants

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How do you know when you’ve reached saturation point? You have to keep conducting interviews or usability tests until you’re no longer uncovering new insights or concepts.

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While this may seem to run counter to the idea of just gathering as much data from as many people as possible, there’s 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, it’s easier for you (the researcher) to build strong close relationships with your participants, which in turn leads to more natural conversations and better data.

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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).

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How your domain affects sample size

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The scope of the topic you’re researching will change the amount of information you’ll need to gather before you’ve hit the saturation point. Your topic is also commonly referred to as the domain.

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If you’re working in quite a confined domain, for example, a single screen of a mobile app or a very specific scenario, you’ll 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.

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As Mitchel Seaman notes: “Exploring a big issue like young peoples’ 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 you’ll want to conduct.”

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In-person or remote

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Does the location of your participants change the number you need for qualitative user research? Well, not really – but there are other factors to consider.

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  • Budget: If you choose to conduct remote interviews/usability tests, you’ll likely find you’ve got lower costs as you won’t need to travel to your participants or have them travel to you. This also affects…
  • 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, instead you can reach out to anyone you’d like.
  • Quality: On the other hand, remote research does have its downsides. For one, you’ll likely find you’re 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.

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Is there value in outsourcing recruitment?

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Recruitment is understandably an intensive logistical exercise with many moving parts. If you’ve ever had to recruit people for a study before, you’ll 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.

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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.

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We’ve got one such service at Optimal, which means it’s the perfect accompaniment if you’re also using our platform of UX tools. Read more about that here.

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Wrap-up

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So that’s 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, it’s actually not all that difficult in reality.

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Overall, the number of participants you need for your qualitative research can depend on your project among other factors. It’s important to keep saturation in mind, as well as the locale of participants. You also need to get the most you can out of what’s available to you. Remember: Some research is better than none!

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Frequently Asked Questions about Optimal’s New Mixed-Methods Usability Testing Tool

We recently hosted a live webinar introducing Optimal's new Usability Testing tool, a powerful solution that brings multiple research methods together in a single study, helping you get better insights, faster.

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Looking for the highlights? We've rounded up answers to the most common questions from the session.

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What is Usability Testing?

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Optimal's new Usability Testing tool is a mixed-methods research tool that brings Prototype Testing, Live Site Testing, and Surveys into a single, end-to-end study workflow. Instead of treating each method as its own initiative, you can combine them inside a single study to allow participants to move naturally between tasks, experiences, and questions.

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With this tool, you can compare multiple prototypes side by side, benchmark a current live experience against a redesigned concept, evaluate a competitor's experience, and more. And researchers get everything analyzed in one place with AI-powered summaries, task results, video clips, and evidence-backed insights surfaced automatically.

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Is Usability Testing supported for mobile testing?

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Yes, participants can complete Usability Testing studies on mobile devices using their mobile browser or the Optimal Participant App. If screen recording is required, participants are prompted to download the Optimal Participant App, available for both iOS and Android. 

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Do you have to use multiple methods, or can you run just one?

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You can keep it simple and run a single survey, a standalone prototype test, or a live site session on its own. Or, mix methods or run multiple of the same method, such as multiple prototypes or live website tests in one study. The tool supports however your study needs to be shaped.

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Can you run bilingual studies?

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Usability Testing currently supports over 30 languages enabling what participants see and guiding how AI models interpret responses, generate summaries, identify themes, and surface insights. Today, studies are configured around a single language, so participants are expected to respond in the chosen language. That said, multilingual study support is something we're exploring for our roadmap.

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Are participants recruited once across all methods, or separately for each?

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Just once. From the participant's perspective, this looks and feels like a single study regardless of how many methods are included. They move through the experience naturally from start to finish.

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To what extent can sections and questions be randomized?

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Section-level randomization shuffles the order of any sections, while question-level randomization works within a specific section, shuffling the order of tasks and follow-up questions. Both are supported, giving researchers the flexibility to reduce order bias, particularly useful when comparing multiple experiences.

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Can you test multiple prototypes within the same study?

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Yes, with no limitations on the number of prototypes you can link to a single study so you can add multiple Figma prototype sections and connect a different prototype to each one.

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Can you reorder sections and questions in a study?

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Given that Usability Testing studies can grow complex, the ability to reorder things quickly was a priority. You can reorder individual tasks and questions within a section, and sections themselves by dragging them in the Build panel.

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How effectively can Usability Testing scale across a business?

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Scaling research isn't just about running more studies, it's about helping more people across the business access insights, understand them, and use them to make decisions. With Usability Testing, product managers, designers, and stakeholders can quickly understand what happened and why without having to see hours of recording through the automatically generated highlight reels, key quotes, and transcripts.

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Watch the full webinar

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If you want to experience the full walkthrough, demo, and Q&A, watch the recording to see Usability Testing in action and pick up tips and best practices straight from the session.

👉 Watch the full webinar here.

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1 min read

Why Participant Recruitment Still Fails, and What Actually Fixes It

Self-serve recruitment made participant recruitment faster and more affordable, but it didn’t completely eliminate the challenge of finding targeted, engaged, and honest participants. In our recent webinar, we called out what 100 research teams said about how they recruit, and used what we learned to build the next evolution of Optimal Recruitment.

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Summary

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  • 75% of research teams say finding the right participants affects study quality or timelines.
  • Self-serve tools made recruitment faster and cheaper, but shifted the work of screening, verification, chasing, and replacing participants
  • 41% of researchers encounter fraudulent participants, while others struggle with participants who match criteria but provide poor-quality responses.
  • Niche audiences are often difficult because multiple common criteria become rare when combined.
  • The fix is a recruitment approach that combines multiple sources with automated checks and human in the loop to find reliable, high-quality participants.

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The 4 biggest challenges of participant recruitment

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1. You can't find the right people

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75% of teams say that not finding the right people impacts either their study quality or their timelines, and two in five have research that simply doesn't happen because they can't source the right participants.

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2. Some participants aren't who they say they are

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41% of researchers run into fraudulent participants, often using VPNs to present as multiple people, and knowledgeable enough to talk vaguely around a topic and slide past quality checks without saying anything specific or true.

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3. The right participant on paper isn't always the right participant in practice

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You can nail the segment, role, and behavior criteria, and still end up with someone who can't articulate a clear thought. That's pushed teams toward workarounds like video screeners to gauge whether someone is introspective and genuinely who they claim to be. Automation is good at matching criteria, but it can’t judge whether someone is introspective and would provide quality data.

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4. Stacked criteria make audiences hard to find

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Many audiences we call niche aren't actually made up of individually rare criteria. It's the combination of requirements that can make someone difficult to find. A specific role, at a certain company size, working in a specific function, using a specific tool are not criteria especially rare on their own. But layered together, the pool can get very small. 

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Solving these challenges takes a platform built to actually find the right people and verify them once they're found. 

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What is self-serve recruitment?

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Self-serve recruitment was created to make participant recruitment faster and easier. Instead of working with an agency, researchers can order participants directly based on the demographics and criteria they need for their study. But while this makes recruitment more accessible, it doesn’t eliminate the work behind the scenes. Teams still have to screen, chase, verify, and replace participants, and four out of five researchers still say the core problem is open.

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Part of the problem is the way self-serve recruitment is typically built. Most tools rely on a single panel and try to make every recruitment request fit within it. Instead, Optimal starts with who you actually need to recruit, then determines where those participants are most likely to be found. We call this a multi-panel model. Some panels are stronger for moderated B2B recruitment, others for general population studies, and others for regional coverage. By combining them, Optimal Recruitment gives you access to 20M+ verified participants across 150+ countries.

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And the data suggests that this broader access matters more than speed alone. In a study of 100 people, only 9% chose faster turnaround as the most important thing to improve. When asked to pick just one thing to fix, they prioritized access to hard-to-reach people, reliability, and better targeting.

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That’s why our focus isn’t just on getting participants into a study quickly. It’s on getting the right participants, from the right sources, with quality built into the recruitment process from start to finish.

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Ensuring participant quality

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Quality checks used to mean if they answered the screener correctly, but increasingly, it's about whether someone understood the task, engaged with it properly, and gave you something useful. Optimal Recruitment has layers of checks so you can find quality participants in every study:

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  • Screeners to filter candidates before they begin your user research study
  • Automated checks to flag straight-lining, repeated answers, and suspicious behavior patterns at scale
  • Human in the loop catches what automation still can't, which matters more as research shifts toward formats like recorded usability tests

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Some teams want to submit an order and get straight into research. Others want more support: screener help, sourcing across panels, manual review, or a fully managed recruit. Neither is the "better" way to recruit. They're solving different problems.

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What we're doing is bringing those two worlds closer together.

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How to make a strong participant screener

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A better screener doesn't necessarily mean a longer screener It's more about being clever with the questions you're asking.

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Add a plausible but wrong option

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Rather than putting an answer or a red herring in that's really obviously fake and easy to spot, we like to include something that sounds like it could be right, but someone with genuine experience should know it isn't.

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Ask the same thing twice but in slightly different ways

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You don't obviously want to literally repeat the question, but you might validate something they told you earlier in the screener from a different angle later. If their experience is genuine, those answers should match up and make sense together. And if they don't, it's a really useful signal to take a closer look at the participant.

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Move more of your instructions into the screener itself, not just in the study

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Clear instructions are a huge contributor to participant quality, but sometimes what looks like a quality issue, it did actually start much earlier where the participant just didn't understand what they were signing up for. For example, in a recorded prototype test, state “this study requires you to speak your thoughts aloud as you complete the tasks, are you comfortable with that and in a quiet space?”; then, people who aren't comfortable can opt out before they ever get into the study.

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FAQ about Optimal Recruitment

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What are participant profiles?

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You can build recruitment profiles which group targeting criteria, like demographics, location, device, job title, seniority, company size, industry, and B2B, as well as screener questions to recruit for your studies. You can also  exclude participants you’ve already spoken to for new perspectives. 

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How many participants is enough?

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It depends on what you’re trying to learn. For usability testing, they tend to surface quickly, so around five participants per user group will often reveal almost all the problems. Concept testing may span a wider context, so you need a larger sample. 

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How do you ensure you are not hearing from the same people?

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We recently have added exclusion controls to participant profiles that lets you automatically exclude participants who've taken part in your studies within a set period; for example, the last three months. This ensures you aren't hearing from the same pool of people.

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How do you work to avoid participant fraud?

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Optimal ensures a 100% quality guarantee for participant responses by utilizing a multi-layered fraud prevention strategy that combines advanced technology with human oversight. Automated systems monitor participant behavior in real-time, detecting "speeders" by monitoring completion times, identifying skipping patterns or "straight-liners," and flagging any inconsistent responses. 

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Our award-winning panel partners maintain a fraud rate of less than 0.06% through advanced machine learning scoring systems (like PureScore) and AI-driven fraud detection, continuously screening participants. For any B2B studies, we will also cross check against LinkedIn profiles.

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Can Optimal help me recruit participants for my next study?

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Yes, Optimal can help you recruit the right participants for your study. You'll see a time estimate for when participants should start coming through after submitting a request.

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Recruitment doesn’t become a bottleneck. Your research can finally start moving at the speed of the questions you're actually trying to answer. 

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👉 If you want to experience the full walkthrough and demo of Optimal Recruitment, watch the full training webinar here.

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1 min read

Tips for recruiting quality research participants

If there’s one universal truth in user research, it’s that at some point you’re going to need to find people to actually take part in your studies. Be it a large number of participants for quantitative research or a select number for in-depth, in-person user interviews. Finding the right people (and number) of people can be a hurdle.

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With the right strategy, you can source exactly the right participants for your next research project.

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We share a practical step-by-step guide on how to find participants for user experience research.

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The difficulties/challenges of user research recruiting 🏋️

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It has to be acknowledged that there are challenges when recruiting research participants. You may recognize some of these:

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  • There are so many channels and methods you can use to find participants, different channels will work better for different projects.
  • Repeatedly using the same channels and methods will result in diminishing returns (i.e. burning out participants).
  • It’s a lengthy and complex process, and some projects don’t have the luxury of time.
  • Offering the right incentives and distributing them is time-consuming.
  • It’s hard to manage participants during long-term or recurring studies, such as customer research projects.

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We’ll simplify the process, talk about who the right participants are, and unpack some of the best ways to find them. Removing these blocks can be the easiest way to move forward.

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Who are the right participants for different types of research? 🤔

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1. The first step to a successful participant recruitment strategy is clarifying the goals of your user research and which methods you intend to use. Ask yourself:

  • What is the purpose of our research?
  • How do we plan to understand that?

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2. Define who your ideal research participant is. Who is going to have the answers to your questions?

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3. Work out your research recruitment strategy. That starts by understanding the differences between recruiting for qualitative and quantitative research.

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Recruiting for qualitative vs. quantitative research 🙋🏻

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Quantitative research recruiting is a numbers game. For your data analysis to be meaningful and statistically significant, you need a lot of data. This means you need to do a lot of research with a lot of people. When recruiting for quantitative research, you first have to define the population (the entire group you want to study). From there, you choose a sampling method that allows you to create a sample—a randomly selected subset of the population who will participate in your study.

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Qualitative recruiting involves far fewer participants, but you do need to find a selection of ‘perfect’ participants. Those that fit neatly into your specific demographic, geographic, psychographic, and behavioral criteria relevant to your study. Recruiting quality participants for qualitative studies involves non-random sampling, screening, and plenty of communication.

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How many participants do you need? 👱🏻👩👩🏻👧🏽👧🏾

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How many participants to include in a qualitative research study is one of the most heavily discussed topics in user research circles. In most cases, you can get away with 5 people – that’s the short answer. With 5 people, you’ll uncover most of the main issues with the thing you’re testing. Depending on your research project there could be as many as 50 participants, but with each additional person, there is an additional cost (money and time).

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Quantitative research is obviously quite different. With studies like card sorts and tree tests, you need higher participant numbers to get statistically meaningful results. Anywhere from 20 - 500 participants, again coming back to the purpose of your test and your research budget. These are usually easier and quicker to implement therefore the additional cost is lower.

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User research recruitment - step by step 👟

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Let’s get into your research recruitment strategy to find the best participants for your research project. There are 5 clear steps to get you through to the research stage:

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1. Identify your ideal participants

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Who are they? What do they do? How old are they? Do they already use your product? Where do they live? These are all great questions to get you thinking about who exactly you need to answer your research questions. The demographic and geographic detail of your participants are important to the quality of your research results.

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2. Screen participants

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Screening participants will weed out those that may not be suitable for your specific project. This can be as simple as asking if the participants have used a product similar to yours. Or coming back to your key identified demographic requirements and removing anyone that doesn’t fit these criteria.

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3. Find prospective participants

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This is important and can be time-consuming. For qualitative research projects, you can look within your organization or ask over social media for willing participants. Or if you’re short on time look at a participant recruitment service, which takes your requirements and has a catalog of available persons to call on. There’s a cost involved, but the time saving can negate this. For qualitative surveys, a great option can be a live intercept on your website or app that interrupts users and asks them to complete a short questionnaire.

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4. Research incentives

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In some cases you will need to provide incentives. This could be offering a prize or discount for those who complete online qualitative surveys. Or a fixed sum for those that take part in longer format quantitative studies.

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5. Scheduling with participants

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Once you have waded through the emails, options, and communication from your inquiries make a list of appropriate participants. Schedule time to do the research, either in person or remotely. Be clear about expectations and how long it will take. And what the incentive to take part is.

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Tips to avoid participant burnout 📛

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You’ve got your participants sorted and have a great pool of people to call on. If you keep hitting the same group of people time and time again, you will experience the law of diminishing returns. Constantly returning to the same pool of participants will eventually lead to fatigue. And this will impact the quality of your research because it’s based on interviewing the same people with the same views.

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There are 2 ways to avoid this problem:

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  1. Use a huge database of potential participant targets.
  2. Use a mixture of different recruitment strategies and channels.

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Of course, it might be unavoidable to hit the same audience repeatedly when you’re testing your product development among your customer base.

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Wrap up 🌯

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Understanding your UX research recruitment strategy is crucial to recruiting quality participants. A clear idea of your purpose, who your ideal participants are, and how to find them takes time and experience. 

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And to make life easier you can always leave your participant recruitment with us. With a huge catalog of quality participants all at your fingertips on our app, we can recruit the right people quickly.

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Check out more here.

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