Types of usability testing

 

 

Diagnostic

Validation

Goal Find design deficiencies Show that the system is usable
Development process Prototype approval during the alpha testing Prerequisite for system deployment,

Part of the product marketing campaign

Means Usability failure detection and analysis Scoring, rating ...
Number of users 3-7 users 50-100 users
Tester's task Observe user difficulties Measure user performance (time and error rates)
References Examples:

http://www.otal.umd.edu/guse/testing.html

http://jthom.best.vwh.net/usability/

The only reference I know is ISO 20282