4.5Customer-Facing Metrics

Mean Time to Recovery (MTTR)

What it measures: The average time to restore service after a failure.

Formula:

MTTR = Total Downtime / Number of Incidents

QA relevance: Faster MTTR often depends on monitoring and alerting that QA helps define. Tests that verify rollback procedures also contribute to lower MTTR.

Mean Time to Failure (MTTF)

What it measures: The average time between system failures.

Formula:

MTTF = Total Uptime / Number of Failures

QA relevance: Better testing (especially performance and reliability testing) directly increases MTTF by catching failure modes before production.

Customer-Reported Defects

What it measures: Defects reported by customers rather than found by the QA team.

Why it matters: Every customer-reported defect is a failure of the testing process. Zero is the ideal. Tracking this metric over time shows whether the QA process is improving at preventing customer-visible bugs.

Formula:

Customer-Reported Defect Rate = Customer Defects / Total Production Defects

If most production defects are customer-reported (rather than caught by monitoring), the team needs better production monitoring in addition to better testing.