Assessment of Conformity, Decision Rules and Risk Analysis
Steven D. Phillips, Michael Krystek
Measurement uncertainty has important economic consequences for calibration and inspection activities. In calibration reports, the magnitude of the uncertainty is often taken as an indication of the quality of the laboratory. In industrial measurements, uncertainty has an economic impact through the decision rule employed in accepting and rejecting products. With significant economic interests at stake, manufacturers have to guard against accepting bad products and rejecting good ones. While the evaluation of measurement uncertainty is a technical activity well described in the GUM, the selection of a decision rule is a business decision that involves cost considerations. Recently, several national and international standards bodies have addressed the decision rule issue to provide a uniform, unambiguous terminology for documenting a decision rule and describe the relationship between the conformance zone (conforming characteristics) and the acceptance zone (acceptable measurement results). Similarly, the issue of risk analysis which addresses the problem of determining the gauging limits (or test limits) that define the boundaries of the acceptance zone and are chosen to balance the risks of the two types of decision errors (accepting nonconforming products and rejecting conforming products), whose relative magnitudes depend upon product-specific economic factors.
Decision Rules, Guard Band, ISO 14253, Conformity Assessment, Risk Analysis