Improved binomial charts for high-quality processes

Abstract

For processes concerning attribute data with (very) small failure rate p, often negative binomial control charts are used. The decision whether to stop or continue is made each time r failures have occurred, for some r ≥1. Finding the optimal r for detecting a given increase of p first requires alignment of the charts in terms of in-control behavior. In the present paper binomial charts are subjected to this same requirement. Subsequent study reveals that the resulting charts are quite attractive in several aspects, such as detection power. For the case of unknown p, an estimated version of the chart is derived and studied.