Human Factors: What's The Difference Between 'Summative' And 'Formative' Usability Testing?

The May 2009 "Silver Sheet" article, "FDA Stresses Human Factors Design For Home-Use Devices," reported that FDA expects a manufacturer to enroll a minimum of 15 subjects when conducting a human factors study.

However, it was not made clear in the article that the agency, when advising the use of 15 subjects, was referring to "summative" human factors testing. Summative testing is a form of device validation that companies use to ensure that user needs have been met