Here's the link I've used before...from Jakob Nielsen. Argue his credibility if you'd like, but in practice I've seen "testing a small number of representative users" as effective as "a lot of random users".
http://www.useit.com/alertbox/20000319.html I haven't seen any justification that 5-6 users is statistically accurate, according to strict mathematical rules, but for practical hands-on work, I'm not entirely sure that's necessary, either. Our six-sigma folks at one company argued heavily that we needed to test 10-20% of a 100K population for statistical accuracy, to which I replied: And meanwhile, we'll test 6-8 folks from each core group and get back to you when we hire an army of practitioners. Bryan Minihan -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Chris Ryan Sent: Thursday, October 01, 2009 2:06 PM To: [email protected] Subject: [IxDA Discuss] Article on Number of Usability Test Participants I have been looking, unsuccessfully, through back issues of interactions magazine for an article, published a few years back, written I believe by someone from Microsoft as part of a debate about statistical significance in usability testing. There was something of a debate about testing with large numbers of users, and this article, as I recall, made an eloquent case for sticking to six to eight participants. Does anyone remember this? Perhaps I'm wrong in recalling that it was in interactions. ________________________________________________________________ Welcome to the Interaction Design Association (IxDA)! To post to this list ....... [email protected] Unsubscribe ................ http://www.ixda.org/unsubscribe List Guidelines ............ http://www.ixda.org/guidelines List Help .................. http://www.ixda.org/help ________________________________________________________________ Welcome to the Interaction Design Association (IxDA)! To post to this list ....... [email protected] Unsubscribe ................ http://www.ixda.org/unsubscribe List Guidelines ............ http://www.ixda.org/guidelines List Help .................. http://www.ixda.org/help
