5 is enough

Usability guru Jakob Nielson argues that you don't need large numbers of testers to gather useful data about an interface. 5 users is sufficient - providing the right trade-off between spotting issues and economy & efficiency.

As you add more and more users, you learn less and less because you will keep seeing the same things again and again. There is no real need to keep observing the same thing multiple times,

Jeez, a whole 5 users?

I guess we'll have to wait a bit before conducting Infocard usability tests.