The written policy a lab and its customer agree on for handling measurement uncertainty in a pass or fail call, for example simple acceptance with a minimum TUR, or guard banding with acceptance limits pulled inside the tolerance by the expanded uncertainty. When a customer asks for a pass or fail statement, the lab agrees the rule before the work and names it on the certificate. The rule sets how the risks of false accept and false reject are shared.
What decision rule do you want on the certs, simple acceptance or guard-banded? It changes how many come back fail.
Related terms
Guard band
A margin that pulls acceptance limits inside the tolerance limits to cut the risk of passing nonconforming items.
Simple acceptance
A decision rule that passes any item whose measured value lies inside the tolerance, leaving uncertainty out of the call.
PFA
Probability of false accept, the chance that a nonconforming item is measured and passed as good.
Specific risk
The probability that one particular measured item is out of tolerance, given its actual measured value.
Tolerance
The allowed deviation from nominal that an item or instrument may show and still be accepted.