For information on the methods used to create the P chart, go to Methods and formulas for P Chart.
The number of plotted points equals the number of samples in your study.
The cumulative % defective for the jth sample is calculated as follows:

The reference lines on the plot are calculated as follows:
For more information on the confidence bounds, go to Methods and formulas for confidence intervals and bounds.
| Term | Description |
|---|---|
| Di | Number of defectives in the ith sample |
| Ni | The ith sample size |