Question

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Why is it important to understand tradeoffs between usability measures for various kinds of systems? Explain by describing usability motivations for Industrial systems and Life Critical systems.

Answer 1

Usability measures

Use a set of well defined criteria/measures that help
to determine the effectiveness and usability of your UI.

It is important to understand the trade-off between usability measures because they help us to check each aspect.

Usability Measures
5 Aspects
1. Time to learn
How long does it take a typical member of your user community
to learn how to use the UI in order to perform the defined tasks?
2. Speed of performance
How long does it take to perform the benchmark tests?
3. Rate of errors by users
How many and what kind of errors do users make in carrying out
the benchmark tasks? (Note: This is related to “speed of
performance”)
4. Retention over time
How well do users maintain their knowledge of how to use
your UI? (Note: This is related to “time to learn”)
5. Subjective satisfaction
How much did users like the UI or certain aspects of it?

Usability Motivation
Industrial systems:
 Example: Banking software, inventory management
systems, human resource management software
(e.g, SAP, PeopleSoft), etc.
 Characteristics
 Costs are a very important factor
 Reliability and operational efficiency is important but not as
crucial as it is with life-critical systems
 Time-to-learn should be low (as it lowers the costs)
 Speed of performance needs to be high (faster operating
speed potentially increases the organization’s profit)
 However, error rates should be low (trade-off with speed)
 Subjective satisfaction is of less concern
 After an initial training period, retention is obtained by very
frequent use.

Usability Motivation
Life-Critical Systems:
 Example: Air-traffic control, medical instruments,
nuclear reactor control, etc.
 Characteristics
 High costs are expected and accepted
 High reliability and effectiveness is a must
 Time-to-learn is commonly high
 High speed of performance and low error rates are crucial
 Subjective satisfaction is of less importance (we deal with
well-motivated professionals)
 Retention is obtained by frequent use and intensive practice