Rigor in Usability Testing
http://www.ingentaconnect.com/content/stc/tc/1999/00000046/00000004/art00007
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  peer-reviewed

Hughes, Michael A.
Technical Communication Online
1999

Abstract:

Usability testing is an evaluation method used by technical communicators that can combine aspects of both quantitative and qualitative research methodologies. This article compares and contrasts the standards and techniques between these two methods of inquiry with particular emphasis on maintaining rigorous tests in regard to validity and reliability of the findings. Whether an evaluator relies on quantitative methods, qualitative methods, or both, should depend on the questions the research or evaluation seeks to answer. Both methods have well-established practices meant to ensure the validity and reliability of their findings. Not only should usability evaluators be competent within the method of inquiry they apply, they also need to help clients understand the legitimate application and limitations of their findings.