Choosing Participants

How many users do you need? 
According to Steve Krug:

  • The ideal number of participants for each round of do-it-yourself testing is three.
  • Some people will complain that three aren’t enough. They’ll say that it’s too small a sample to prove anything and that it won’t uncover all of the problems.

Krug believes both complaints are true but asserts that doesn’t matter because:

  • The purpose of this kind of testing isn’t to prove anything.
  • You don’t need to find all of the problems.

Jakob Nielsen has long asserted that 5 users is the proper number, for similar reasons as Krug.

I think most experts will recommend starting with 3-5 participants, although, like user research, the best number is “Until you are no longer learning.”

Finding Participants
In the business world, you may have a number of ways to find research participants from among customers, company clients, professional recruiters, and even employees. But for your personal project, first look to your social media and professional contacts.

For your personal project:

  • Places like coffee shops and malls have plenty of participants to offer. If you’re having trouble getting anyone’s attention, consider offering gift cards from a local shop or restaurant. 
  • Tap into your network. Many designers are willing to swap user tests or feedback. 
  • If you’re in an office building, consider making friends with your neighbors. One researcher carried her laptop down to test a prototype with the receptionist two floors below. The participant even let the test be recorded so the researcher could share it with her team.
  • As a last resort, consider family and friends. Their feedback will come heavily biased so this is probably best for a quick usability test and not much more. 

In the business world you’ll want to be more stringent about the participants you’ll use. One exception to this rule is when you are testing early versions of an interface and are just seeking some general feedback. In that case, you might test with whoever is available that can give you some representative feedback.

Common Testing Pitfalls
Here are some common pitfalls when recruiting participants and how to avoid them.

Pitfall: Failing to identify the correct user groups to include in testing.

To avoid: Predetermine which user groups to include in the testing.

Pitfall: Failing to screen participants properly or recruiting professional focus-group participants, who are only in it for the money.

To avoid: Decide what important characteristics define your user groups. Use those characteristics to screen potential participants and ensure they are representative of your users.

Don’t get caught up in recruiting by demographics, unless there are important demographics that define your user groups. For example, income probably isn’t that important when testing a retail pharmacy’s Web site, but it would be very important in testing an expensive, luxury cruise liner’s Web site.

Pitfall: Testing with friends, family members, and coworkers, simply because they’re easily available, even though they may not fit the profile of the users.

To avoid: use lists of existing users—whether customers, members, or employees—whenever you can. These people are already actual users and require little, if any, screening.

Pitfall: Relying on a client to recruit participants, but not providing them with enough information about who to recruit and who to avoid.

To avoid: Provide your clients with details about the types of people to recruit and those to avoid.

im Ross’s insights into the biggest mistakes in usability testing includes a number of participant-related issues.

Learn more about fast and cheap ways to find participants