ISO 9241

Ergonomic requirements for office work with visual display terminals

ISO 9241 deals with the specification and evaluation of usability giving special attention to the user interface, e.g. visual display terminals (VDT's). In this way it addresses software product evaluation since usability and the user interface are important issues when evaluating the quality of a software product.

Information regarding ISO 9241 is provided under the following headings:

the target audience
an abstract of the standard
the relationship between ISO 9241 and ISO 9126

Audience

The intended audience for this document is:

software product suppliers, in order to help them develop ergonomically sound visual display terminals and software products;
purchaser of software products, in order to help them specify more thoroughly VDT's for the use in their own organisation;
those who wish to evaluate the usability and user guidance of (existing) software products.

Abstract

ISO 9241 establishes the ergonomic requirements for office work with VDTs in order that the VDT users can operate display screen equipment safely, effectively, and comfortably. The standard is clearly user-oriented since ISO 9241 emphasises the need to specify the factors affecting the performance of the user (which can be expressed in terms of effectiveness, efficiency and satisfaction), and to asses user performance as a basis for evaluating whether or not a system is appropriate to the context in which it will be used. This standard claims ambitiously that "it is also relevant to those who wish to assess the suitability of existing equipment, working environments and work practices".

In view of the complexity of VDT ergonomics and the complex and multipurpose nature of ISO 9241, it has been organised into a number of parts, each dealing with a different aspect of VDT use. For software product evaluation the most relevant parts are:

Part 1 "General"

This part gives an overview of the intended purpose and scope of the 9241 series;

Part 11 "Guidance on usability specification and measures"

This part defines usability and explains how it can be specified and measured. Part 11 explains how to identify the information necessary to specify usability in terms of measures of user performance and satisfaction. It provides a decomposition of the components of the context of use into sub-components (user, task, equipment, environment), with measurable and verifiable attributes. In order to be able to measure usability, Part 11 also provides a decomposition of usability measures consisting of target or actual values of effectiveness, efficiency, and satisfaction for the intended context.

Part 13 "User guidance"

This part provides recommendations for the design and evaluation of user guidance attributes of software user interfaces, in particular prompts, feedback, error management and on-line help. These recommendations are presented as a checklist which can be used as guidance when specifying requirements for the product or as criteria when evaluating it. ISO 9241 - Part 13 can be used as an evaluation module for attributes of user interfaces.

ISO 9241 versus ISO 9126

ISO 9241 - Part 11 deals with usability, which is one of the six quality characteristics defined in ISO 9126. However, the definitions provided by both standards are different:

ISO 9241: usability: "the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use"
ISO 9126: usability: "a set of attributes that bear on the effort needed for use, and on the individual assessment of such use, by a stated or implied set of users"

Looking at the definitions is should be clear that ISO 9241 has a broader view on usability than ISO 9126, because it also explicitly puts weight on tasks and environmental issues like organisational factors. Usability as defined in ISO 9241 also depends on software qualities that are distinct from usability as defined in ISO 9126, such as functionality, reliability and efficiency, e.g. time behaviour. These software qualities all contribute to quality of the software product in use.