ISO definition: The extent to which a system, product or service can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use.
Note: Technical defects (bugs) are also usability problems if they prevent users from solving their tasks effectively or efficiently.
For examples, see the sections on effectiveness, efficiency and satisfaction below.
ISO definition: A user’s perceptions and responses that result from the use and/or anticipated use of a system, product or service.
The following figure illustrates the relationship between usability, user experience, effectiveness, efficiency and satisfaction:
Example that illustrates the similarities and differences between usability and user experience:
When ordering flowers for delivery from a flower store’s website:
- Usability problems encountered during checkout affect both the user experience and usability.
- The quality of the physical flowers delivered affects only the user experience. It does not affect usability of the flower store’s website.
- The experience of visiting the physical store affects the user experience of subsequent visits to the website. It does not affect the usability of the flower store’s website.
ISO definition: The accuracy and completeness with which users achieve specified goals.
Popular, unofficial definition: Can it do what * I * want?
Example 1: A car rental website does not offer users any opportunity to cancel a reservation. An analysis of the context of use shows that users need this function. There is a problem with the effectiveness of the website.
Example 2: A car rental website enables users to cancel a reservation. A usability test shows that only 5 out of 100 users are able to figure out how to cancel their reservation. Those who are able to figure out how to do it, do so quickly. There is a problem with the effectiveness of the website.
ISO definition: The resources used in relation to the results achieved.
Popular, unofficial definition: Can it solve my tasks reasonably fast?
Example 1: A car rental website enables users to cancel a reservation. A usability test shows that the cancellation procedure is needlessly complicated even though all usability test participants finally manage to cancel their reservations. The effectiveness of the website is OK, since all users manage to achieve their goal. There is a problem with the efficiency of the website.
Example 2: Sluggish response caused for example by an overloaded interactive system is a usability problem
ISO definition: The extent to which the user’s physical, cognitive and emotional responses that result from the use of a system, product or service meet the user’s needs and expectations.
Popular, unofficial definition: Do I feel safe and well while using the interactive system?
Examples of satisfaction and dissatisfaction:
Example 1: Users spontaneously say that they like the appearance of the home page of a car rental website (satisfaction).
Example 2: Users say that it “takes forever” to reserve a car on a car rental website (dissatisfaction).
Example 3: Prolonged periods of use of a notebook without an external mouse causes muscular discomfort (dissatisfaction).
Note: High prices or unacceptable terms of service in a web shop are not part of satisfaction because satisfaction is about the usage of an interactive system. They may influence the user experience.
Context of use
ISO definition: A combination of users, goals, tasks, resources, and environments.
Example of context of use, users, goals and tasks, environments and resources:
Consider the interactive system “messaging app”: Teenagers on a bus use their phones to send messages to their friends to make them laugh.
a. Users: Teenagers;
b. Goal: Make friends laugh;
c. Task: Send message;
d. Social environment: Friends:
e. Physical environment: Bus;
f. Resource: Phone.
For definitions of users, goals, tasks, resources, and environments, please refer to the CPUX-F curriculum.
Source of definitions
The definitions and examples are taken from the ISO 9241-11 standard and from the CPUX-F curriculum. The CPUX-F curriculum is freely available on www.uxqb.org
Text from the international standard ISO 9241-11.2018, Usability: Definitions and concepts, is reproduced with permission from Danish Standards Foundation (DS)