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This is one of those things that takes a very abstract concept and tries to boil it down a bit too far with a mathematical model. Also, the 5 number in the head

This is one of those things that takes a very abstract concept and tries to boil it down a bit too far with a mathematical model. Also, the 5 number in the headline is just misleading, since he clearly points out that the real number is 15. The reality is that the number of people you need to test with to get the right number of insights (along with the depth of testing for any given user) is going to vary drastically across products of varying purposes and level of complexity. 5/15 users may be a reasonable average, but this is a case where an average of many different things isn't a particularly useful measure for any one of those things. That doesn't even take into account the quality of people that you're testing with. Five experienced testers is different than five people with domain expertise but not testing experience is different than five people off the street.

zild3d 7y ago
> Also, the 5 number in the headline is just misleading, since he clearly points out that the real number is 15. The 5 number isn't misleading at all, the author shows that it's the 80/20 point. The first 5 users in your usability test give you 85% of the value of testing with 15. The takeaway is to not do the same exact test with 15 users, do an iteration with 5, and rinse and repeat. "Let us say that you do have the funding to recruit 15 representative customers and have them test your design. Great. Spend this budget on 3 studies with 5 users each!"