Defect Detection Percentage
Defect Detection Percentage (DDP) measures the proportion of total defects that are found during a specific testing phase before release.
“The number of defects found by a test level, divided by the number found by that test level and any other means afterwards.”
(Definition reproduced from the ISTQB Glossary. Copyright belongs to ISTQB.)
View the complete ISTQB GlossaryWhat is Defect Detection Percentage?
A higher DDP indicates that testing activities are effective at identifying defects before customers encounter them in production.
Calculation: Compares defects found during testing with the total defects found before and after release.
Quality indicator: Helps evaluate testing effectiveness.
Continuous improvement: Trends identify opportunities to strengthen testing processes.
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. Defect detection percentage 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 Defect detection percentage helps everyone discuss the problem using a shared testing vocabulary.
Practice Questions
Question 1
Which statement BEST describes Defect detection percentage in the context of ISTQB terminology?
Question 2
A tester needs to explain Defect detection percentage to a non‑technical stakeholder. Which approach is MOST appropriate?
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