Question: The ISO 9241 standard Ergonomics of Human-System Interaction (ISO, 2008) focuses on admirable goals-effectiveness, efficiency, and satisfaction-but the following usability measures, which focus on the latter two goals, lead more directly to practical evaluation:

1. Time to learn. How long does it take for typical members of the user community to learn how to use the actions relevant to a set of tasks?

2. Speed of performance. How long does it take to carry out the benchmark tasks?

3. Rate of errors by users. How many and what kinds of errors do people make in carrying out the benchmark tasks? Although time to make and correct errors might be incorporated into the speed of performance, error handling is such a critical component of interface usage that it deserves extensive study.

4. Retention over time. How well do users maintain their knowledge after an hour, a day, or a week? Retention may be linked closely to time to learn, and frequency of use plays an important role.

5. Subjective satisfaction. How much did users like using various aspects of the interface? The answer can be ascertained by interviews or by written surveys that include satisfaction scales and space for free-form comments.

Select 1 of the 5 measures above and provide a description of WHY you believe it is essentially important in designing User Interfaces.

All responses must be 300-350 words.