Conformity assessment of processes and lots in the framework of JCGM 106:2012

Abstract

ISO/IEC 17000:2020 defines conformity assessment as an "activity to determine whether specified requirements relating to a product, process, system, person or body are fulfilled". JCGM (2012) establishes a framework for accounting for measurement uncertainty in conformity assessment. The focus of JCGM (2012) is on the conformity assessment of individual units of product based on measurements on a cardinal continuous scale. However, the scheme can also be applied to composite assessment targets like finite lots of product or manufacturing processes, and to the evaluation of characteristics in discrete cardinal or nominal scales. We consider the application of the JCGM scheme in the conformity assessment of finite lots or processes of discrete units subject to a dichotomous quality classification as conforming and nonconforming. A lot or process is classified as conforming if the actual proportion nonconforming does not exceed a prescribed upper tolerance limit, otherwise the lot or process is classified as nonconforming. The measurement on the lot or process is a statistical estimation of the proportion nonconforming based on attributes or variables sampling, and meassurement uncertainty is sampling uncertainty. Following JCGM (2012), we analyse the effect of measurement uncertainty (sampling uncertainty) in attributes sampling, and we calculate key conformity assessment parameters, in particular the producer's and consumer's risk. We suggest to integrate such parameters as a useful add-on into ISO acceptance sampling standards such as the ISO 2859 series.