An average can summarize the past and still hide the mechanism destroying reliability.
Why the average can mislead
MTBF often assumes that failure behavior is sufficiently stable. Young, deteriorating or repairable assets—or assets subject to changing context and multiple failure modes—may require a different interpretation.
Questions before calculation
- What event counts as a failure?
- What is the population and exposure period?
- Are data censored, truncated or incomplete?
- Are there different failure modes?
- Is the system restored “as good as new” or “as bad as old”?
- Did load, product, environment or policy change?
The right analytics depend on the decision
Life data and Weibull analysis can support interval or survival decisions. Repairable-system models can reveal growth or deterioration. RAM can test architecture, capacity and redundancy. Simulation and sensitivity can make uncertainty and trade-offs explicit.
The exit criterion
The analysis should end in a design, task, frequency, spares, policy or risk decision—not a chart without an owner.
Statistics do not replace asset knowledge. They force it to become explicit and testable.