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 Recommended methods: 5. Usability requirements

 

Methods
Basic
Recommended
   0. Maturity assessment
   1. Stakeholder meeting
   2. Context of use
   3. Task scenarios
   4. Test existing system
   5. Usability requirements
   6. Paper prototyping
   7. Style guides
   8. Evaluate prototype
   9. Usability testing
 10. Collect feedback
      Specialised methods

– Satisfaction questionnaires
– Web site design
– Instructional systems design
– List of methods
– Integration with development

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Purpose

To establish usability requirements which can be tested later in the development process.

Benefits

  • Highlights the importance of usability early in development
  • Provides concrete objectives for usability
  • Provides usability criteria that can be tested.

Method

1. Quality in use requirements

Establish requirements for effectiveness, efficiency and satisfaction for the user groups and tasks identified in the context of use analysis and in the scenarios.

Arrange a workshop attended by:

  • user(s)
  • developer(s).

You will also need a facilitator and a person to record the issues raised during the meeting.

  • Review each of the tasks in the context analysis report along with their associated task scenarios to confirm their relevance and importance.
  • Decide which task(s) and user type(s) needed usability criteria.

For each chosen task and user type estimate:

  • the acceptable task time and the optimum target
  • how to score effectiveness by agreeing what errors the user might make
  • the effectiveness target
  • the satisfaction target.

If there is an existing system, it can be evaluated by the selected users and tasks, and the results used to refine the usability requirements. Quality in use requirements should be evaluated by usability testing.

Example

"Data entry clerks will be able to input data from the forms with 98% accuracy in a mean time of less than 10 minutes. The mean offsiteSUMI score will be greater than 50."

More information on quality in use requirements

More information on setting criteria for effectiveness, efficiency and satisfaction can be found in ISO 9241-11: Guidance on usability, and ISO/IEC 9126-4: Quality in use metrics ("quality in use" is defined is a similar way to "usability" in ISO 9241-11).

2. Detailed usability requirements

Decide which usability requirements are relevant. Examples of potential requirements are:

Understandability

  • Interface elements (e.g. menus) should be easy to understand
  • For a walk up and purchase or use system, the purpose of the system should be easily understandable

Learnability

  • The user documentation and help should be complete
  • The help should be context sensitive and explain how to achieve common tasks
  • The system should be easy to learn

Operability

  • The interface actions and elements should be consistent
  • Error messages should explain how to recover from the error
  • Undo should be available for most actions
  • Actions which cannot be undone should ask for confirmation
  • The system be customisable to meet specific user needs
  • A style guide should be used

Attractiveness

  • The screen layout and colour should be appealing

Arrange a workshop to review how to elaborate the requirements for the specific system being developed. The workshop should be attended by:

  • developer(s)
  • user(s) if easily available

You will also need a facilitator and a person to record the issues raised during the meeting.

Usability requirements should be evaluated when testing a paper or machine prototype.

Example

The Microsoft Windows style guide will be adhered to. Error messages must give the user specific instructions for recovery. The help system will explain all functions and how to achieve common tasks. Users will be able to consistently locate appropriate help information. All keyboard shortcuts will be customisable.

More information on usability requirements

Detailed design should adhere to a GUI or web style guide.

There are international standards for usability and user centred design. ISO 9241 contains guidelines for the design of office systems. Examples of usability metrics are given in ISO/IEC TR 9126-2: Internal metrics and ISO/IEC TR 9126-3: External metrics, due to be available in 2001.

Next steps

Evaluate any existing systems, then use mock ups and paper prototypes to clarify the requirements for the new system.

Last updated 19-Nov-00

 

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