Software Usability

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Software Usability

• Re-focusing Software as the Tool

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Understanding Usability
In order to understand the term usability, we
must first understand some referential terms
which precede usability in terms of system design

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System Acceptability
from Nielsen, Jakob. Usability Engineering.
Morgan Kaufmann1993.
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Usability ComponentsLearnability

• System should be easy to learn
• Users should be able to get things done quickly
  after learning
• How do we measure learnability?
• Is the user able to complete a certain task or
  set of tasks successfully?
• What does successfully mean?

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Usability ComponentsEfficiency of Use

• The level of an expert users performance after
  the learning curve flattens
• This is termed the steady state of performance
  (I.e. Productivity has not increased
  considerably over a specified amount of time)
• How do we measure efficiency of use?
• Define the experienced user
• Define some definition of expertise
• Test the amount of time it takes the user to
  complete a given task or set of tasks

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Usability ComponentsMemorability

• Somewhat a measure for casual users
• Tied to learnability, but different
• How do we measure memorability?
• Method 1 Test performance of casual users on
  tasks once they have been away from the system
  for a specified amount of time
• Method 2 Memory test of users, asking them to
  explain common tasks

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Usability ComponentsLow Error Rate

• Error Any action that does not accomplish the
  desired goal (Nielsen)
• Error rates should be categorized Minor Errors
  and Catastrophic Errors
• How do we measure error rate?
• Count the instances of errors by users while
  performing a certain task or group of tasks
• Do not include errors which are immediately
  corrected by the user

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Usability ComponentsSubjective Satisfaction

• How pleasant it is to use the system
  (Nielsen)
• Important factor for systems used on a
  discretionary basis (entertainment systems,
  etc.)
• Related to user experience of peak difficulty
  in using the system
• How do we measure subjective satisfaction?
• Tests of physical indicators (heart rate, etc.)
• Simple survey of users
• Related measure Approachability (the users
  perception of how hard/easy it would be to learn
  a new system

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Usability Slogans

• Your best guess is not good enough.
• The user is always right
• The user is not always right
• Users are not designers
• Designers are not users
• Vice-Presidents are not users
• Less is more.
• Details matter.
• Help doesnt.
• Usability engineering is a process.

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Resources

• Nielsen, Jakob. Usability Engineering. Morgan
  Kaufmann 1993.

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Questions?