What is Usability?
Usability is a quality attribute that assesses how easy user interfaces are to use. It's defined by five key components:
Learnability
How easy is it for users to accomplish basic tasks the first time they encounter the design?
Efficiency
Once users have learned the design, how quickly can they perform tasks?
Memorability
When users return after a period of not using it, how easily can they reestablish proficiency?
Errors
How many errors do users make, how severe are they, and how easily can they recover?
Satisfaction
How pleasant is it to use the design?
Nielsen's 10 Usability Heuristics
Visibility of System Status
The system should always keep users informed about what is going on through appropriate feedback within reasonable time.
Match Between System and Real World
The system should speak the users' language, with words, phrases, and concepts familiar to the user.
User Control and Freedom
Users often choose system functions by mistake and need a clearly marked "emergency exit" to leave the unwanted state.
Consistency and Standards
Users should not have to wonder whether different words, situations, or actions mean the same thing.
Error Prevention
Even better than good error messages is a careful design which prevents a problem from occurring in the first place.
Recognition Rather Than Recall
Minimize the user's memory load by making objects, actions, and options visible.
Flexibility and Efficiency of Use
Accelerators may speed up interaction for expert users, allowing the system to cater to both inexperienced and experienced users.
Aesthetic and Minimalist Design
Dialogues should not contain information which is irrelevant or rarely needed.
Help Users Recognize, Diagnose, and Recover from Errors
Error messages should be expressed in plain language, precisely indicate the problem, and constructively suggest a solution.
Help and Documentation
It's best if the system can be used without documentation, but it may be necessary to provide help and documentation.
Core Design Principles
Affordances
An affordance is a relationship between the properties of an object and the capabilities of the user that determine how the object could be used. Buttons should look clickable, sliders should look draggable.
Feedback
Users should receive immediate and clear feedback about the result of their actions. This confirms that the system has received their input and is processing it.
Constraints
Limiting the possible actions helps prevent errors. Physical, cultural, and logical constraints guide users toward correct usage.
Mapping
The relationship between controls and their effects should be clear and logical. Natural mapping takes advantage of spatial analogies.
Usability Testing Methods
🎯 Heuristic Evaluation
Experts review the interface against established usability principles to identify potential issues.
- Quick and cost-effective
- Can be done early in design
- Identifies many issues
👥 User Testing
Real users perform tasks while observers watch and take notes to identify usability problems.
- Reveals real user behavior
- Uncovers unexpected issues
- 5-8 users find most problems
📊 A/B Testing
Compare two versions of a design to see which performs better with actual users.
- Data-driven decisions
- Tests specific hypotheses
- Requires traffic volume
🗣️ Think Aloud Protocol
Users verbalize their thoughts while using the interface, revealing their mental model and expectations.
- Reveals user reasoning
- Identifies confusion points
- Low-cost method
Test Your Knowledge
Question 1
Which usability component measures how easy it is for users to accomplish tasks on their first encounter?
Question 2
Which heuristic states that users need a clearly marked "emergency exit" when they make mistakes?
Question 3
What design principle describes the relationship between an object's properties and how it can be used?
Question 4
Which testing method involves experts reviewing an interface against established principles?
Question 5
Which heuristic emphasizes that dialogues should not contain irrelevant information?