The standard posits that usability is not a single metric, but a composite of three distinct outcome measures. A product is only considered "usable" if it balances all three.
A hospital MRI machine might be effective (produces a clear scan) and efficient (takes 10 minutes), but if the patient experiences claustrophobia and extreme discomfort (low satisfaction), the overall usability is poor. iso 9241-11 standard definition of usability
Efficiency is measured relative to effectiveness. It is not enough to simply complete the task; the cost of that completion matters. Resources can include time, mental effort (cognitive load), physical effort, and even financial cost. The standard posits that usability is not a
Perhaps the most critical element of the ISO 9241-11 definition is the phrase "in a specified context of use." The standard argues that usability is not an intrinsic property of a product. A powerful data analysis tool that is highly usable for a trained data scientist (effective and efficient for complex queries) will be completely unusable for a first-time visitor. The context includes the (their skills, knowledge, and experience), their goals (what they are trying to accomplish), the environment (physical, social, and technical conditions), and the equipment (hardware, software, and peripherals). A smartphone app designed for use on a crowded, noisy subway train (a context of high distraction) requires a different usability profile than the same app used at a quiet desk. Efficiency is measured relative to effectiveness