024 P & NP Control Charts - Control Charts for Attribute Data - What, Why, How, and When to use

P and NP control charts are statistical process control charts that are used to monitor the proportion of nonconforming items (defectives) and the number of nonconformities (defects) in a process, respectively.
The P control chart is used to monitor the proportion of nonconforming items in a sample of constant size. It is based on the binomial distribution and plots the proportion of nonconforming items in each sample over time. The chart has control limits that are calculated based on the expected variability in the proportion of nonconforming items.
The NP control chart is used to monitor the number of nonconformities in a sample of variable size. It is based on the Poisson distribution and plots the number of nonconformities in each sample over time. The chart has control limits that are calculated based on the expected variability in the number of nonconformities.