Comparing Assessment Techniques
http://www.stc.org/ConfProceed/1993/PDFs/Pg354355.pdf

Redish, Janice C. 'Ginny'
STC Proceedings
1993

Abstract:

In just the last few years, we have begun to see research studies comparing usability testing to other techniques for assessing usability. In general, usability testing has found more of the most serious usability problems and fewer of the least serious problems than other methods. Heuristic evaluation--having people evaluate the interface either from their own expertise or from a set of guidelines--has achieved mixed results. Although usability testing seems expensive compared to other methods, it may be less expensive when considered on the basis of 'cost per problem that needs to be fixed.'