Usability and Quality

Quality is an attribute of a product or service is misleading, as the attributes required for quality will depend on how the product is used.
Quality of use is therefore defined as the extent to which a product or service satisfies stated and implied needs when used under stated conditions. Quality of use can be used to measure usability as the extent to which specified goals can be achieved with effectiveness, efficiency and satisfaction by specified users carrying out specified tasks in specified environments.

1. What is usability?

Web usability as an objective is synonymous with quality of use, ie that the web site can be used in the real world. Thus usability has two complementary roles in design: as an attribute which must be designed into a web site, and as the highest level quality objective which should be the overall objective of design.

What is quality?

There is a close analogy between different interpretations of the term usability and comparable interpretations of the term quality. Although the term quality seems self-explanatory in everyday usage, in practice there are many different views of what it means and how it should be achieved as part of a web production process.

A simple analysable property which is recognised through experience

Usablequality: an inherent characteristic of the web site determined by the presence or absence of measurable functional and content attributes.

Production quality: a web site which conforms to specified requirements.

User perceived quality: the combination of web site attributes which provide the greatest satisfaction to a specified user.

If different groups of users have different needs, then they may require different characteristics for a web site to have quality, so that assessment of quality becomes dependent on the perception of the user.

ISO 9126 takes this approach and categorises the attributes of software quality as: functionality, efficiency, usability, reliability, maintainability and portability.

Quality and usability Comparison

Some compare usability to quality assurance. There are important similarities: Both seek to improve system quality; both are cost-effective; both can reduce development time. However, they are not identical.
Usability focuses on the user interface, on the elements the end user directly interacts with, and the quality-of-use issues users directly encounters: screen layout, colors, menus, error messages; consistency, navigation, orientation, etc. Usability engineering's purpose is to enhance the quality of the end-user's experience while quality assurance focuses on elements that users do not interact with directly, such as code integrity. Quality assurance is now familiar to most software professionals, but most software professionals are not as familiar with usability engineering.

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