Usability
Usability is the degree to which specified users can use a product effectively, efficiently, and satisfactorily to achieve specified goals in a specified context of use.
“The degree to which a component or system can be used by specified users to achieve specified goals in a specified context of use.”
(Definition reproduced from the ISTQB Glossary. Copyright belongs to ISTQB.)
View the complete ISTQB GlossaryWhat is Usability?
Usability focuses on making software easy to learn, understand, operate, and remember while minimizing user errors.
User focused: Measures ease of use.
Quality characteristic: Defined by ISO standards.
Experience driven: Strongly influences user satisfaction.
Real World Example
A hospital rolls out a new nurse charting tablet app to replace paper charts, and the app passes every functional test with zero bugs reported.
Nurses take twice as long to log vitals compared to paper, several give up mid-task and grab a colleague for help, and post-shift interviews reveal real frustration — none of which a clean functional bug report ever measures.
The tester designs a genuine Usability evaluation: recruiting actual nurses, not QA staff, to attempt real charting tasks under realistic ward-like time pressure, measuring task completion rate, time on task, number of errors, and a satisfaction rating afterward — alongside, not instead of, functional testing.
The study reveals the vitals entry screen requires seven taps where paper took one motion, directly explaining the slowdown — a usability defect invisible to functional testing but decisive for whether the rollout actually succeeds on the ward floor.
Practice Questions
Question 1
A hospital charting app passes every functional test with zero bugs, but nurses take twice as long to log vitals as they did on paper and several give up mid-task. Which quality concern does this MOST directly point to?
Question 2
Which combination of measures BEST reflects a genuine usability evaluation, rather than just a functional check?
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