A New $p$-Control Chart with Measurement Error Correction

TL;DR

This paper introduces a new $p$-control chart that corrects for measurement errors, providing more accurate monitoring of non-conforming product proportions, especially with small samples, improving detection reliability.

Contribution

It proposes a novel error-corrected EWMA $p$-control chart with asymmetric limits, addressing measurement errors and small sample challenges in quality control.

Findings

The corrected chart effectively eliminates measurement bias.

Simulation results confirm improved detection accuracy.

Asymmetric limits enhance sensitivity for small samples.

Abstract

Control charts are important tools to monitor quality of products. One of useful applications is to monitor the proportion of non-conforming products. However, in practical applications, measurement error is ubiquitous and may occur due to false records or misclassification, which makes the observed proportion different from the underlying true proportion. It is also well-known that ignoring measurement error effects provides biases, and is expected that the resulting control charts may incur wrong detection. In this paper, we study this important problem and propose a valid method to correct for measurement error effects and obtain error-eliminated control chart for the proportion of non-conforming products. In addition, unlike traditional approaches, the corrected EWMA $p$-control chart provides asymmetric control limits and is flexible to handle the data with small sample size. Numerical results are conducted to justify the validity of the corrected EWMA $p$-control chart and verify the necessity of measurement error correction.