Use NP Chart to monitor the number of defective items where each item can be classified into one of two categories, such as pass or fail. Use this control chart to monitor process stability over time so that you can identify and correct instabilities in a process.
For example, a delivery service manager uses an NP chart to monitor the number of delivery vehicles that are out of service each day for 2 months. A vehicle that is out of service is considered a defective unit.
The chart shows that, on average, 25 of the delivery vehicles are out of service each day. The number of defective units for day 19 is out of control. The manager should identify any special causes that contribute to the unusually high number of defectives.
To create an NP chart, choose .