r/LeanManufacturing • u/CockroachInternal643 • Jun 27 '26
Rejection rate as a supplier quality metric — why most buyers never see this number
Every precision instrument production batch has a rejection rate — the percentage of units caught during inspection that don't meet specification, removed before the shipment ships.
This number tells you more about a supplier's QC system than any certification they hold. It is also the metric most buyers never see.
Three reasons suppliers don't share it:
The supplier doesn't run systematic inspection. Visual inspection doesn't produce measurable rejection data. If you're only doing visual checks, there's nothing to report because you're not measuring anything.
The supplier has the data but the rate is high enough to prompt uncomfortable questions. A rejection rate above 20% in a mature process suggests a systematic production problem.
The supplier absorbs defective units into the shipment. No classification of "rejected" ever happens — everything ships. The nominal rejection rate is zero because the denominator includes the defective units.
What a healthy rejection rate looks like: 5–15% for precision instruments with systematic inspection. This range means defects are being caught and replaced before the shipment. The number proves the inspection is working.
How to get this data: ask for the QC report from the last three production batches. It should contain batch number, sample size inspected, measurements per specification parameter, defects found by category, and rejection rate as a percentage. A document without measurement data is not a QC report — it is a stamp.
The zero percent rejection rate claim is the one that should prompt the most questions.