FIT5152 Chap.1 Defining and Measuring Usability
Defining and Measuring Usability
Week 1 of FIT5152 sets up the idea the whole unit depends on: usability is never a fixed property of an interface. A booking screen that a daily commuter finishes in seconds can defeat a tourist using a borrowed phone in the rain.
The standard definition, from ISO 9241-11, therefore ties usability to specified users, specified goals and a specified context of use, and judges it through effectiveness, efficiency and satisfaction.
The seminar adds a working rule that follows directly: when you design or evaluate a product, name at least one target or actual measure for each of those three components.
The chapter then compares that standard with two practitioner models. The Nielsen Norman Group lists learnability, efficiency, memorability, errors and satisfaction, while Whitney Quesenbery’s five Es add engagement and error tolerance.
Each model makes you notice something different, such as how quickly a returning user recovers proficiency. The last part sorts out four terms that often blur together: human–computer interaction as the field, the user interface as the information and controls, user experience as perceptions before, during and after use, and user-centred design as the practice of keeping users and context in view at every stage.
You also meet the three roles the seminar describes in a product team: usability engineer, interface designer and software developer.
What this chapter covers
- 01
The ISO 9241-11 usability definition
- 02
Effectiveness, efficiency and satisfaction measures
- 03
Nielsen Norman Group quality components
- 04
Quesenbery’s five Es
- 05
HCI, UX, UI and user-centred design
- 06
Usability engineer, interface designer and developer roles
Worked example · free
Choosing one measure per ISO component for a library-room booking app
- 1Effectiveness: the percentage of booking attempts that end in a confirmed room, set as a target of most attempts succeeding first time.
- 1Efficiency: median seconds from opening the app to confirmation, measured as an actual value in testing with a small group of students.
- 1Satisfaction: post-task ratings of how stressful booking felt, plus the aspects students say they liked or disliked.
Key terms
- Usability
- The extent to which specified users can achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use.
- Effectiveness
- The accuracy and completeness with which users achieve specified goals.
- Efficiency
- The resources, such as time or effort, spent in relation to the effectiveness achieved.
- Memorability
- How easily users regain proficiency when they return to a design after a period away from it.
- User Experience
- How a person perceives and reacts to a product, system or service, whether in actual or expected use.
- User-Centred Design
- A design approach that keeps the specified users and their context of use in view at every stage of development.
Defining and Measuring Usability FAQ
Why does the ISO definition insist on specified users and goals?
Because a design can work well for one group doing one task and badly for another. Naming the users, goal and context makes a usability claim testable instead of a general impression about whether a product is nice.
How many usability measures should a design or evaluation include?
The Week 1 seminar asks for at least one measure, either a target or an actual value, for each of the three ISO components: effectiveness, efficiency and satisfaction.
What do the Nielsen Norman Group components add to the ISO list?
They separate out learnability for first use, memorability for returning users and errors, covering how many occur, how severe they are and how easily users recover, which ISO folds into its broader components.
Is user experience the same as the user interface?
No. The interface is the information and controls a system provides, while user experience covers expectations before use, experiences during use and perceptions afterwards, so it reaches beyond the screen.
Assessment move
Learn the ISO definition word for word first, then practise unpacking it on products you used today. For a ride-share app, a banking app and a museum ticket kiosk, write the specified users, one goal and the context, then add one measure per component and label each as a target or an actual value.
Next, build a three-column comparison of ISO, the Nielsen Norman Group components and the five Es from memory, marking which ideas appear in only one model. Finally, rehearse the four overlapping terms by explaining aloud, in under a minute, how HCI, UI, UX and user-centred design differ. These definitions resurface in every later week, so the time you spend now pays back in Submission 1 when you justify questionnaire choices.
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