Failure Rate
Failure rate is a reliability metric that measures how frequently failures occur within a specified period of operation or usage.
“The ratio of the number of failures of a given category to a given unit of measure.”
(Definition reproduced from the ISTQB Glossary. Copyright belongs to ISTQB.)
View the complete ISTQB GlossaryWhat is Failure Rate?
Organizations use failure rate to evaluate system reliability, monitor quality trends, and estimate operational performance over time.
Reliability measurement: Lower failure rates generally indicate higher reliability.
Trend monitoring: Failure rates can reveal quality improvements or deterioration.
Operational metric: Often measured during production or reliability testing.
Real World Example
A hospital medication system shows a different dosage warning in test than the one specified by the clinical safety rule.
The team needs precise language to separate what was observed, what should have happened, and whether the difference represents a reportable issue. Failure rate provides that distinction.
The tester records the steps, data, observed behavior, expected behavior, and evidence so triage can focus on patient safety impact instead of vague descriptions.
The issue is handled faster because Failure rate helps everyone discuss the problem using a shared testing vocabulary.
Practice Questions
Question 1
Which statement BEST describes Failure rate in the context of ISTQB terminology?
Question 2
A tester needs to explain Failure rate to a non‑technical stakeholder. Which approach is MOST appropriate?
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