Imagine a usability test where five out of five participants completed all tasks successfully. What are the chances that 50 or 1000 will have a 100% completion rate? By calculation confidence intervals, you will be able to tell that the chances lies somewhere between 95% and as low as 48%.

In his article, Jeff Sauro shows us how calculate confidence intervals of usability tests.

Links:

• The article Restoring Confidence in Usability Results

Henrik Olsen - July 08, 2004

See also: Usability testing (28)  Tips and guidelines (63)