← QCE Digital Solutions Unit 1

Useability principles for evaluating a user interface

Criteria for judging a prototype's interface: accessibility, effectiveness, error tolerance, ease of learning and engagement, rated using evidence from a user trial.

Part of: QCE Digital Solutions Unit 1 — Programmed Solutions — Module 112

Understanding Useability principles for evaluating a user interface in QCE Digital Solutions Unit 1

What it does: Large text and high contrast colours are accessibility features a tester can check in a prototype. A completion rate gives measurable trial evidence to rate effectiveness. Error tolerance is about preventing mistakes or letting users recover from them easily, for example with confirmations or undo. Ease of learning is judged by how quickly first-time users can work out the interface. Observed times and help requests are trial evidence. A rating should be justified with evidence from a trial, such as observations, counts or tester comments, not just personal opinion. Engagement is how interesting and motivating the interface is to use, so that users stay involved.

Common mistakes: == compares two values and does not store one. principle is never created, so the later print causes a NameError. It should be principle = 'engagement'. A function definition must end with a colon. It should be def rate(score):.

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This module's key terms are also in a printable crossword (Modules 158–380) and word search (Modules 82–380).

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Learning

Duo

A tester with low vision can read all text in a prototype because it uses large, high-contrast fonts. Which useability principle is being met?

AccessibilityEngagement

Matches

Rating: Engagement = Good (no trial evidence given)

↓

The rating has no evidence from a user trial. It should be supported, for example: 8 of 10 testers said the game was fun and kept playing.

Applying

Meanings

Term

useability principles

Meaning

Criteria for judging a prototype's interface: accessibility, effectiveness, error tolerance, ease of learning and engagement, rated using evidence from a user trial.

Practice

Accessibility: 5 of 5 users read the text - Rating 4/5

Testing

Gaps

principle = ""

Check Answer

Spots

1principle == 'engagement'

2rating = 3

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Quick Questions

1. A tester with low vision can read all text in a prototype because it uses large, high-contrast fonts. Which useability principle is being met?

A. Engagement

B. Accessibility ✓

Accessibility means people with different needs, such as low vision, can use the interface. Large, high-contrast text supports this.

2. A user accidentally taps Delete and the app shows 'Undo' and 'Are you sure?'. Which principle does this support?

A. Error tolerance ✓

B. Ease of learning

Error tolerance is about preventing mistakes or letting users recover from them easily, for example with confirmations or undo.

3. Which is the best evidence for rating ease of learning in a user trial?

A. Time taken by new users to finish a task with no help ✓

B. The number of colours used in the design

Ease of learning is judged by how quickly first-time users can work out the interface. Observed times and help requests are trial evidence.

4. A user trial shows 9 out of 10 testers completed the booking task correctly. Which principle is this evidence mostly about?

A. Accessibility

B. Effectiveness ✓

Effectiveness is whether users can complete tasks accurately and achieve their goals. A completion rate is direct evidence.

5. Which statement is a useability rating backed by evidence?

A. Error tolerance: 4/5, as 8 of 10 testers recovered from a wrong entry using the Undo button ✓

B. Error tolerance: 4/5, because I think the design looks good

A rating should be justified with evidence from a trial, such as observations, counts or tester comments, not just personal opinion.

Match the Pairs

Error tolerance → A usability principle: the interface prevents mistakes or helps users recover from them, for example with a confirm box or an undo option.

Ease of learning → A usability principle: a new user can work out how to use the interface quickly, with little or no training.

Accessibility is judged by checking whether people with different needs can use the interface, such as through readable text size and strong colour contrast. → font=('Arial', 18), fg='black', bg='white'

Effectiveness is rated with evidence from a user trial, such as how many testers completed the task correctly. → Task completed: 9 of 10 testers = 90%

Rating: Engagement = Good (no trial evidence given) → The rating has no evidence from a user trial. It should be supported, for example: 8 of 10 testers said the game was fun and kept playing.

Delete button: deletes the record straight away, no warning → This is poor error tolerance. A confirm box such as 'Are you sure?' or an undo option should be added so accidental clicks can be recovered from.

Key Term

useability principles

Criteria for judging a prototype's interface: accessibility, effectiveness, error tolerance, ease of learning and engagement, rated using evidence from a user trial.

Fill in the Blanks

1. principle = "accessibility" print(principle, "is for everyone")

Hint: Type the useability principle about letting people with different abilities and needs use the interface.

2. rating = {} rating["effectiveness"] = "All 5 tasks done"

Hint: Type the principle that checks whether users can complete their tasks successfully.

3. minutes = 4 if minutes < 5: rating = "Good ease of learning"

Hint: Type the keyword that starts a decision, so a rating is only given when the learning time is short.

4. principles = ["accessibility", "engagement"] for principle in principles: print(principle)

Hint: Type the keyword that starts a loop going through each item in the list.

5. evidence = "4 of 5 users made no errors" print("Error tolerance:", evidence)

Hint: Type the function name that shows the rating and its trial evidence on screen.

Spot the Error

Question 1

A principle == 'engagement'

B rating = 3

C evidence = 'Stayed on task'

D print(principle, rating)

Line A — == compares two values and does not store one. principle is never created, so the later print causes a NameError. It should be principle = 'engagement'.

Question 2

A def rate(score)

B if score >= 4:

C return 'Good'

D return 'Needs work'

Line A — A function definition must end with a colon. It should be def rate(score):.

Question 3

A contrast_ok = False

B if contrast_ok:

C print('Easy to read')

D else

E print('Low contrast')

Line D — else needs a colon after it to start its block. It should be else:.

Question 4

A age = input('Age: ')

B while age.isdigit():

C print('Digits only')

D age = input('Age: ')

Line B — The loop should repeat while the input is NOT valid, so the user gets another go after a mistake (error tolerance). Without not, it skips bad input. It should be while not age.isdigit():.

Question 5

A completed = 8

B total = '10'

C rate = completed / total * 100

D print(f'Completed: {rate}%')

Line B — total is a string, so dividing by it causes a TypeError. The task completion rate (effectiveness) needs a number. It should be total = 10.

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