---
alias: user-guide-fraction-defective
description: "This documentation details a statistical chart for monitoring defect rates"
---

# Fraction Defective (p)

The following table lists the properties of the Fraction Defective (p) chart.

| Property                                            | Description                                                       |
|-----------------------------------------------------|--------------------------------------------------------------------|
| **Chart**                                           | Fraction Defective *(p)*                                                                                                        |
| **Process observation types**                       | Attributes                                                                                                                  |
| **Process observations relationships**              | Independent                                                                                                                 |
| **Sample Size**                                     | Variable, usually \>=50                                                                                                     |
| **Distribution type**                               | Binomial                                                                                                                    |
| **Size of shift to detect**                         | Large (≥ 1.5σ)                                                                                                              |
| **Fraction Defective (Indicator 1)**              | $p=\frac{number\;of\;rejects}{number\;inspected}$                                        |
| **Fraction Defective (Indicator 2)**              | ***Not applicable***                                                                                                            |
| **Standard Deviation for sample**   | $s = \sqrt{\frac{\overline{p}(1-\overline{p})}{n}}$<br/>Where $\overline{p}$ is the centerline and $n$ is the sample size which can vary by sample |
| **Fraction Defective (Indicator 1) Centerline**     | $\overline{p}=\frac{total\;number\;of\;rejects}{total\;number\;inspected}$ |
| **Fraction Defective (Indicator 1) Control Limits** | $UCL = min(\overline{p}+3s;1)$<br/>$LCL = max(\overline{p}-3s;0)$ |
| **Indicator 2 Centerline**                          | ***Not applicable***                                                                                                            |
| **Indicator 2 Control Limits**                      | ***Not applicable***                                                                                                            |

Table: Fraction Defective chart properties