u Chart in Excel
Use a u chart when counting defects and when the sample size varies
The purpose of a u chart is to determine stability of "counted" data (e.g., errors per bill, dents in a car door, etc.) when there can be more than one defect per unit and the sample size varies.
Defects (u charts) vs Defective Items (p charts):
- Defects - each item in a sample can have more than one defect (e.g. dents on a car door, errors on a bill, missing products in a shipment).
- Defective items: Each item is only counted once (e.g. car doors that need to be repainted, bills that are wrong, incomplete shipments, C-sections in a delivery),
u chart data looks like this:
To create a u chart in Excel using QI Macros:
- Just click and drag over the data to select it.
- Then click on the QI Macros menu, Control Charts, then u chart.
- QI Macros will all of the math and draw the u chart for you. QI Macros will also turn any unstable points or conditions on the u chart red. These should be investigated.
Example of a u chart created using QI Macros for Excel
The stair step or skyline control limits are the result of the varying sample sizes.
- u chart template in Excel
- u chart formulas
- Other Attribute Control Charts in Excel
- What is a Control Chart?