SYSE.36:5.2 - Turn a definition into a decision, not just a percentage

For a separate arithmetic illustration, suppose the responsible users/providers agree that at least 99% of a named service’s eligible tasks must satisfy its complete good-result definition over a specified 30-day window. They also agree how budget exhaustion changes the priority of reliability work. This is an illustrative agreement, not a recommended universal target.

With 1,000 fully observed eligible tasks, 995 good and 5 bad, the observed ratio is 99.5%. The window’s 1% allowance is 10 bad tasks, so the five consume half of that event budget. Neither the arithmetic nor five further available events permits violation of an independent data-integrity requirement.

Now suppose ten results are missing rather than fully observed. The same exact reliability claim is no longer established merely by keeping the old ratio on the dashboard. Recover the observations or apply the agreed missing-data policy with that limitation visible. If the service sees only ten events in an hour, high-volume alert thresholds require a separate fit decision; the number 99% does not supply it.

What changes in practice is that an observed failure, an unobserved task and an agreed reliability trade-off lead to different decisions for the right service.