p chart

**P chart** is the **attributes control chart used to monitor the proportion of nonconforming units in samples over time** - it is the standard SPC method for defectives-rate surveillance when sample size may vary. **What Is P chart?** - **Definition**: Chart of defective fraction calculated as defectives divided by total inspected units per sample. - **Data Type**: Binary classification per unit, such as conforming versus nonconforming wafer. - **Sample Flexibility**: Supports variable sample sizes with corresponding dynamic control-limit adjustment. - **Statistical Basis**: Uses binomial-process assumptions for centerline and limit estimation. **Why P chart Matters** - **Quality Visibility**: Provides direct trend view of defectives rate at line and tool levels. - **Containment Speed**: Rising defective fraction can trigger fast quality intervention. - **Operational Scalability**: Practical for high-volume inspection streams with simple classification outputs. - **Compliance Support**: Creates auditable record of quality-rate stability over time. - **Complementary Analytics**: Works alongside defect-count charts for fuller quality insight. **How It Is Used in Practice** - **Classification Discipline**: Maintain consistent criteria for defective disposition across inspectors and shifts. - **Limit Maintenance**: Recompute limits when baseline performance or sampling plan changes materially. - **Response Workflow**: Connect P-chart signals to hold, review, and corrective-action procedures. P chart is **a foundational SPC chart for nonconformance-rate control** - robust defective-fraction monitoring is critical for yield governance and early quality-risk detection.