Capability Analysis (Poisson) generates process capability report for attribute data that follows the Poisson distribution. The report includes a
U Chart to verify if the process is in statistical control
Cumulative mean DPU chart to verify if the data have a consistent estimate of mean
Histogram of DPU to help visualize the distribution of DPU of the sample data
Defect Rate Chart to verify that the DPU is not affected by the sample size
Poisson Plot (when subgroup size is constant) to verify that the expected number of defects are not affected by the observed number of defects
The most common types of Poisson data are records of defects per unit. In order the use Capability Analysis (Poisson), you need to ensure that the following assumptions are valid:
The rate of defects is the same for each unit
The number of defects in each unit is independent of each other
At the Excel Menu (For Excel 2007, go to Add-ins first)
Choose ProcessMA > Quality Tools > Capability Analysis > Capability Analysis (Poisson)
In Defects, select the column containing the data (Integer, >=0)
In Sample Sizes, select the column containing sample sizes (Integer, >Defectives)
In Constant Sample Size, enter the sample size if it is constant (Optional, Integer, >Defectives)
In Historical Mean , enter the population mean (Optional, Numeric)
In Target DPU, enter the target DPU value (Optional, Numeric)
Click OK
You work in a refrigerator manufacturing plant. You need to ensure that the surface of the refrigerators is in good condition. You inspect a random surface area of 100cm2 of each refrigerator and recorded the number of scratches and dents found.
Open data worksheet by choosing ProcessMA > Tools > Data
Choose ProcessMA > Quality Tools > Capability Analysis > Capability Analysis (Poisson)
In Defects, select AG - Scratches
In Constant Sample Size, enter 100
The U Chart shows that there are several points out of control. The Cumulative DPU chart shows that the overall DPU settles at 0.023.
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