ITPEC FE Morning October 2021 Question 23

Usability — ISO 9241-11 defines it by effectiveness, efficiency and satisfaction for specified users, goals and context of use.

The three measures are effectiveness (goals achieved accurately and completely), efficiency (resources spent for the result) and satisfaction (the user's comfort with and attitude to the use). Usability is always relative: the same product can be usable for one group of users and tasks and not for another.

Answer (d)

Why not others:

• •(a) Accessibility — the extent to which a product can be used by people with the widest range of needs, characteristics and capabilities, such as users with disabilities
• •(b) Adaptability — the ability of a system to be adjusted to different users, environments or requirements
• •(c) Availability — being ready for use when needed, usually measured as the share of time the system is working

Key rule: The trio effectiveness, efficiency and satisfaction in a specified context of use is the ISO definition of usability; accessibility widens who can use a product, usability measures how well they can.

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