Question: How many users do you need to test with for a usability test?
Answer 1: = 5 users (Jakob Nielsen and Thomas Landauer, 1993).
Answer 2: = 15 users (Laurie Faulkner, 2004), PDF file.
So, which is it, 5 or 15? And why are we arguing about an extra 10 users, doesn't one need to test with at least 100 or more users for statistical significance, accuracy and validity?