Recruit at least 50 participants per user group. 100 is ideal. You’ll need more if each participant is only shown a subset of the tasks.
If you use web ads to get participants, choose web pages (and even other websites) that target the kinds of users you’re looking for.
Web ads should be designed to attract attention and present an at-a-glance proposition, and should link to a page that briefly explains the study and provides an obvious way to start.
If you email invitations, be sure to qualify the recipients as well as you can, and send your invitations in batches to conserve your participant pool.
If you use social media, consider which channels are appropriate, and keep your invitation short and punchy.
If you use commercial research panels, choose those that adequately cover your region and the types of users you’re looking for.
To boost numbers and reduce selection bias, use a variety of methods to recruit your participants.
Make sure you’re getting the participants you want by filtering your customer lists and/or screening those who see your invitation.
Recipients are more likely to participate if they receive a clear invitation from a sender they know.
For most studies, offer an incentive. Prize draws are usually easiest.
Next: Chapter 10 - Piloting the test