U-Chart is an attribute control chart used when plotting:

- DEFECTS
- POISSON ASSUMPTIONS SATISFIED
- VARIABLE SAMPLE SIZE (subgroup size)

Each observation is independent. This chart is used to develop an upper control limit and lower control limit (UCL/LCL) and monitor process performance over time. It plots the **number of defects per unit sampled in a variable sized sample.**

If defect level is small, use the Poisson Distribution exact limits, DPU < 1.5.

Used to detect shifts >1.5 standard deviations. In order to detect smaller shifts there are other charts that can be applied to variable and attribute data such as Exponentially Weighted Moving Average (EWMA) and Cumulative Sum of Quality Characteristic Measurement (CUSUM).

Most statistical software programs automatically calculate the UCL and LCL to quickly examine control offer visual insight to the performance over time.

Shown below is the data set plotted using a U-Chart.

The chart indicates that the process is in control. The control tests that were used all passed in this case.

Recall there are a variety of control tests and most statistical software programs allow you to select and modify these criteria.

Return to SPC Charts

Return to the MEASURE phase

Return to the CONTROL phase

Templates and Calculators

Return to the Six-Sigma-Material Home Page

Click for a Password

to access entire site

Templates & Calculators

**Six Sigma Modules**

The following presentations are available to **download**

**Click Here**

*
Green Belt Program 1,000+ Slides
Basic Statistics
SPC
Process Mapping
Capability Studies
MSA
Cause & Effect Matrix
FMEA
Multivariate Analysis
Central Limit Theorem
Confidence Intervals
Hypothesis Testing
T Tests
1-Way Anova Test
Chi-Square Test
Correlation and Regression
SMED
Control Plan*