← QCE Digital Solutions Unit 2

Useability principles for an interface

Six criteria for judging an interface: accessibility, effectiveness, ease of learning, efficiency, error tolerance and engagement. A good interface does well on all of them.

Part of: QCE Digital Solutions Unit 2 — Prototype Data Solutions — Module 90

Understanding Useability principles for an interface in QCE Digital Solutions Unit 2

What it does: A keyboard shortcut cuts the number of steps needed, so the task is done faster. That is efficiency. A familiar icon with a clear label helps first-time users understand what to do straight away. That is ease of learning. Accessibility means people with different abilities and needs can use the interface, for example through readable text, strong contrast and screen reader support. Accessibility, effectiveness, ease of learning, efficiency, error tolerance and engagement are the criteria used to evaluate an interface. Error tolerance means a slip, such as a wrong click, does not cause big problems because the user can undo it or is warned first.

Common mistakes: The label's for value must match the input's id (age). Without a matching id, screen readers can't link the label to the box, which hurts accessibility. It should be for="age". A confirmation step gives error tolerance, but 'not' makes the item delete when the user says no. It should be: if confirm("Sure?"):.

Class: _____________________ · Name: _____________________ · Date: _________

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This module's key terms are also in a printable crossword (Modules 337–409) and word search (Modules 234–409).

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Learning

Duo

A form has large text, high-contrast colours and works with a screen reader. Which useability principle does this show?

Error toleranceAccessibility

Matches

Delete button removes a student record at once with no warning and no undo

↓

Poor error tolerance: one accidental click permanently loses data. Add a confirmation message or an undo option.

Applying

Meanings

Term

useability principles

Meaning

Six criteria for judging an interface: accessibility, effectiveness, ease of learning, efficiency, error tolerance and engagement. A good interface does well on all of them.

Practice

accessibility: can everyone use it?

Testing

Gaps

Check Answer

Spots

1<form>

2<label for="name">Age</label>

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Quick Questions

1. A form has large text, high-contrast colours and works with a screen reader. Which useability principle does this show?

A. Accessibility ✓

B. Error tolerance

Accessibility means people with different abilities and needs can use the interface, for example through readable text, strong contrast and screen reader support.

2. An app shows a message 'Are you sure you want to delete this?' and lets users undo a deletion. Which principle is this?

A. Error tolerance ✓

B. Ease of learning

Error tolerance means the interface prevents mistakes where it can and makes it easy to recover when they happen, for example with confirmations and undo.

3. A school canteen app lets a regular user reorder their usual lunch in two taps. Which principle is this?

A. Efficiency ✓

B. Accessibility

Efficiency is about how quickly and with how little effort an experienced user can finish a task, such as using shortcuts and fewer steps.

4. A new user can work out how to book a library room without reading a manual because the labels and icons are familiar. Which principle is this?

A. Efficiency

B. Ease of learning ✓

Ease of learning is how quickly a first-time user can understand and use the interface without training or help.

5. True or false: Useability principles are used to judge how well an interface works for its users.

A. False

B. True ✓

Accessibility, effectiveness, ease of learning, efficiency, error tolerance and engagement are the criteria used to evaluate an interface.

Match the Pairs

Accessibility → Everyone can use the interface, including people with vision, hearing or movement difficulties

Error tolerance → The interface prevents mistakes and makes it easy to recover from them

Efficiency: users finish a task quickly with few steps → Ctrl+S saves a file in one step

Ease of learning: a new user can work out how to use it without much training → A magnifying glass icon labelled Search

Delete button removes a student record at once with no warning and no undo → Poor error tolerance: one accidental click permanently loses data. Add a confirmation message or an undo option.

Light grey text on a white background with no alt text on images → Poor accessibility: low contrast and missing alt text make the screen hard to read for users with low vision or screen readers. Use high contrast and add alt text.

Key Term

useability principles

Six criteria for judging an interface: accessibility, effectiveness, ease of learning, efficiency, error tolerance and engagement. A good interface does well on all of them.

Fill in the Blanks

1. <img src="logo.png" alt="School logo">

Hint: Type the attribute that gives screen reader users a text description of an image, supporting accessibility.

2. try: age = int(input("Age: ")) except ValueError: print("Numbers only")

Hint: Type the exception name raised when text cannot be converted to a number, so the program shows error tolerance.

3. <input type="text" autofocus>

Hint: Type the attribute that puts the cursor in the field automatically, saving the user a step and improving efficiency.

4. <input type="text" placeholder="dd/mm/yyyy">

Hint: Type the attribute that shows a sample format inside an empty field, which helps ease of learning.

5. <label for="email">Email address</label> <input id="email" type="email">

Hint: Type the attribute that links a label to the input with the matching id, which supports accessibility for assistive technology.

Spot the Error

Question 1

A <form>

B <label for="name">Age</label>

C <input id="age" type="number">

D </form>

Line B — The label's for value must match the input's id (age). Without a matching id, screen readers can't link the label to the box, which hurts accessibility. It should be for="age".

Question 2

A def delete_item(item):

B if not confirm("Sure?"):

C item.remove()

D show("Item deleted")

Line B — A confirmation step gives error tolerance, but 'not' makes the item delete when the user says no. It should be: if confirm("Sure?"):

Question 3

A print("1. Add student")

B print("3. Remove student")

C print("3. Show students")

D choice = input("Choose 1-3: ")

Line B — Two options are numbered 3, so the menu is confusing and hard to learn. A clear, consistent menu makes the interface easy to learn. This line should be numbered 2.

Question 4

A user = load_saved_user()

B if user is not None:

C address = user.phone

D else:

E address = input("Addr: ")

Line C — A saved user's address should be reused so they don't retype it, which makes the interface efficient. This line wrongly uses the phone number. It should be user.address.

Question 5

A body {

B font-size: 16px;

C color: #222;

D background: #333;

E }

Line D — Dark grey text (#222) on a dark grey background (#333) has very low contrast, so many users can't read it. Accessibility needs strong contrast, such as a white background (#fff).

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