In this paper, after having stated the basic benefits of usability, the authors examine the evidence for a positive ROI. They list key usability benefits, then define appropriate value propositions. For each of these value propositions, they present examples from the literature that help to interpret the cost of usability challenges and/or they cite statistics.

While a cost-benefit analysis for every circumstance does not exist, these “proofs” of applying usability in user interfaces predict likely quantifiable benefits or ROI.

Return on Investment for Usable User-Interface Design:Examples andStatistics (PDF)