p-Charts for Attribute Control

In this article, we introduce charts for attribute control considering the number of defective items, named np-charts. These charts are preferable over charts for proportion (p) of defective items, named p-charts, when the sample size (n) remains constant for all subgroups. The benefits of using np-charts over p-charts are: an easier interpretation and the fact that no calculation is required for each sample result. We provide a review of the basic issues related to np-charts and some recent ideas on the topic based on life distributions. In addition, we discuss an implementation of np-charts in the R software by using examples with data on attributes and lifetimes. Keywords: binomial distribution; life distributions; p-charts; R software