Which metric is used to estimate the average time between failures in reliability data analysis?

• A. Failure rate
• B. MTBF
• C. Availability
• D. Reliability index

Answer: (B)

Mean Time Between Failures measures the average operating time a repairable system runs before a failure occurs. It’s the go-to metric in reliability data analysis when you want to understand how long a system typically operates before needing repair, since after each failure the item is fixed and put back into service, creating a sequence of operating intervals. MTBF is calculated as the total operating time divided by the number of observed failures, giving a practical sense of the expected time between breakdowns.

Failure rate describes how often failures occur per unit time (a hazard rate), which isn’t the same as the average interval between failures. Availability looks at the proportion of time the system is up versus down, incorporating both uptime and downtime, not the specific gap between failures. The reliability index is a broader measure and not the standard metric for average time between failures.