Discount usability engineering

Learnability evaluation has traditionally required expensive and time-consuming techniques. Practitioners have refrained from performing extended learnability evaluation due to its prohibitive costs. We propose a discount method for evaluation of an interactive system's learnability. Our method is based on automated logging of user actions, detection of user mental chunks, and observation of chunk size as it grows over time with experience. We introduce a model for chunk detection, and present experimental results validating the use of chunk size as an indicator of learnability.