Decision Rule

Decision Rule

The decision rule for the statement of conformity is based on the “Zero Guard Band Rule/Simple Acceptance” in accordance to ILAC-G8:09/2019 and IEC Guide 115:2021, unless otherwise be required by the standard or requested by the customer. This means that measurement uncertainty is not taken into account and hence also not be declared in the test report. In this case, statement of conformity is made according to whether the measured result is below the tolerance limit without considering the measurement uncertainty, reported as “Pass” or “Fail”. See Figure 1 below.

“Zero Guard Band Rule”/”Simple Acceptance” is also called “shared risk”. When assuming a symmetric normal distribution of the measurements, the probability of false acceptance/rejection may be as high as 50% in the case when a measured result is exactly on or near the tolerance limit. In another word, the risk that accepted items are outside the tolerance limit is up to 50%, and the risk of false reject is up to 50% for measured results outside the tolerance.

Reference document

ILAC-G8:09/2019 Guidelines on Decision Rules and Statements of Conformity