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Goal vs. Testable NFR

publish date: 2026/06/05 21:07:10.559098 UTC

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Consider these two statements about system usability:

Goal: The system should be easy to use by medical staff and should be organized in such a way that user errors are minimized.

Testable NFR: Medical staff shall be able to use all the system functions after four hours of training. After this training, the average number of errors made by experienced users shall not exceed two per hour of system use.

Why is the Testable NFR preferred over the goal?

The testable NFR is shorter and therefore clearer

The testable NFR provides measurable, objectively verifiable criteria; the goal is vague and cannot be tested

The testable NFR was written by an engineer, while the goal was written by a user

The testable NFR focuses on training time, which is always the most important usability metric

Correct Answer

The testable NFR provides measurable, objectively verifiable criteria; the goal is vague and cannot be tested

Explanation

Whenever possible, non-functional requirements should be written quantitatively so they can be objectively tested. The goal sets good intentions but cannot be verified. The testable NFR gives concrete thresholds (4 hours training, ≤2 errors/hour) that can be measured during system evaluation.

Reference

Software Engineering, Ian Sommerville, 9th edition

Quizzes you can take where this question appears

Functional and Non-Functional Requirements