Joe’s First Computer Encounter

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(Joe reads the text on IE and clicks on “Suggested Sites”)

Me: “Why did you click on that?”

Joe: “I don’t really know what to do, so I thought this would suggest something to me.”

Finding adults who’ve got basically no computer experience whatsoever is getting increasingly rare (and already was very uncommon back in 2011 when this was written), and so I can see why Jennifer Morrow, when presented with the serendipitous opportunity to perform some user testing with one, made the very most of the occasion.

As well as being a heart-warming story, this post’s a good reminder that we shouldn’t make assumptions about the level of expertise of our users.

Why You Only Need to Test with 5 Users

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Some people think that usability is very costly and complex and that user tests should be reserved for the rare web design project with a huge budget and a lavish time schedule. Not true. Elaborate usability tests are a waste of resources. The best results come from testing no more than 5 users and running as many small tests as you can afford.

In earlier research, Tom Landauer and I showed that the number of usability problems found in a usability test with n users is:

N (1-(1- L ) n )

where N is the total number of usability problems in the design and L is the proportion of usability problems discovered while testing a single user. The typical value of L is 31%, averaged across a large number of projects we studied. Plotting the curve for L =31% gives the following result…

Diminishing returns for usability testing, as more and more users are tested. The curve bends around 5 users, which is the recommended number of test participants.