## Calculating A Sigma Level From Task Success

###### By Jeff Sauro, PhD . September 17, 2004 . Tags: Six Sigma

Often the most reported measures of usability is task success. Success rates can be converted into a sigma value by using the discrete-binary defect calculation: Proportion Unsuccessful= Defects/Opportunities Where opportunities are the total number of tasks and defects are the total number of unsuccessful tasks. This calculation provides a proportion that is equivalent to a success or failure rate. For example, if 143 total tasks