Chapter 4 – Performance Metrics

Publisher Summary Performance metrics are powerful tools to evaluate the usability of any product. Performance metrics are always based on participants' behavior rather than what they say. There are five general types of performance metrics. Task success metrics are used when one is interested in whether participants are able to complete tasks using the product; in whether a user is successful or not based on a strict set of criteria; or in defining different levels of success based on the degree of completion, the experience in finding an answer, or the quality of the answer given. Time-on-task is a common performance metric that measures how much time is required to complete a task. Errors are a useful measure based on the number of mistakes made while attempting to complete a task. Efficiency is a way of evaluating the amount of effort required to complete a task. Efficiency is often measured by the number of steps or actions required to complete a task or by the ratio of the task success rate to the average time per task. Learnability involves looking at how any efficiency metric changes over time and is useful in examining how and when participants reach proficiency in using a product. Performance metrics rely not only on user behaviors but also on the use of scenarios or tasks.