Why You Only Need To Test With 5 Users

Why You Only Need to Test with 5 Users

  • November 15, 2010

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:

The most striking truth of the curve is that zero users give zero insights.

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User Community And ROI

User Community and ROI

  • July 31, 2009

Every time I give a talk, someone always asks, ”That’s all good and nice that helping users learn is the key to creating passionate users… but who’s going to do all that extra work? Who’s going to make the extra tutorials and better docs?” Answer: your user community.

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