Reliability Growth Model
A reliability growth model is a mathematical model used to estimate how software reliability improves as defects are identified and corrected during testing.
“A model that shows the growth in reliability over time of a component or system as a result of the defect removal.”
(Definition reproduced from the ISTQB Glossary. Copyright belongs to ISTQB.)
View the complete ISTQB GlossaryWhat is Reliability Growth Model?
These models help predict future reliability, estimate remaining defects, and determine release readiness.
Statistical model: Uses historical failure data.
Continuous improvement: Reliability increases as defects are removed.
Release support: Assists in release planning and risk assessment.
Real World Example
A national travel service is preparing for a public holiday sale where thousands of users may search, reserve, and pay for tickets at the same time.
A feature that works for one tester may fail under traffic, resource pressure, or infrastructure disruption. Reliability growth model helps the team focus on behavior under operational conditions.
The tester defines realistic traffic, failure, and recovery situations, then watches response time, errors, data consistency, and whether users can continue critical actions.
The release decision improves because Reliability growth model gives stakeholders evidence about service behavior when demand or disruption is no longer theoretical.
Practice Questions
Question 1
Which statement BEST describes Reliability growth model in the context of ISTQB terminology?
Question 2
A tester needs to explain Reliability growth model to a non‑technical stakeholder. Which approach is MOST appropriate?
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