Overview for P Chart

Use P Chart to monitor the proportion 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 a P chart to monitor the proportion of delivery vehicles that are out of service each day for 2 months. A vehicle that is out of service is considered a defective item. The chart shows that, on average, 8% of the delivery vehicles are out of service on any particular day. The proportion of defective units for day 19 is out of control. The manager should identify any special causes that contribute to the unusually high rate of defectives.

Where to find this control chart

  • PC: STATISTICS > Control Charts > Attribute > P
  • Mac: Statistics > Attribute > P

When to use an alternate control chart

If you can count the number of defects on each item, use U Chart to plot the number of defects per unit.

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