Hypothesis-based acceptance sampling for modules F and F1 of the European Measuring Instruments Directive

TL;DR

This paper re-interprets the acceptance sampling conditions of the EU's MID modules F and F1, proposing a statistically sound, hypothesis-based approach that improves economic efficiency and applicability to small lots.

Contribution

It introduces a new hypothesis-based interpretation of MID sampling conditions, enhancing statistical rigor and applicability to finite-sized lots.

Findings

Bounded producers' risk at 95% confidence

Alignment with formal hypothesis testing framework

Effective for very small lot sizes

Abstract

Millions of measuring instruments are verified each year before being placed on the markets worldwide. In the EU, such initial conformity assessments are regulated by the Measuring Instruments Directive (MID). The MID modules F and F1 on product verification allow for statistical acceptance sampling, whereby only random subsets of instruments need to be inspected. This paper re-interprets the acceptance sampling conditions formulated by the MID. The new interpretation is contrasted with the one advanced in WELMEC guide 8.10, and three advantages have become apparent. Firstly, an economic advantage of the new interpretation is a producers' risk bounded from above, such that measuring instruments with sufficient quality are accepted with a guaranteed probability of no less than 95 %. Secondly, a conceptual advantage is that the new MID interpretation fits into the well-known, formal framework of statistical hypothesis testing. Thirdly, the new interpretation applies unambiguously to finite-sized lots, even very small ones. We conclude that the new interpretation is to be preferred and suggest re-formulating the statistical sampling conditions in the MID. Re-interpreting the MID conditions implies that currently available sampling plans are either not admissible or not optimal. We derive a new acceptance sampling scheme and recommend its application.