## Margins of Error in Usability Tests

###### By Jeff Sauro . August 6, 2009 . Tags: Margin of Error, Task Metrics, Statistics

How many users will complete the task and how long will it take them? If you need to benchmark an interface, then a summative usability test is one way to answer these questions. Summative tests are the gold-standard for usability measurement. But just how precise are the metrics? Just as a presidential poll uses a sample to estimate outcomes for the entire population, usability tests