The Laney U' chart is similar to the Laney P' chart in its use. We use this chart when we have the Poisson data that shows evidence of overdispersion or underdispersion. As the steps for use of the Laney U' chart are very similar to the P' chart, we will not use an example dataset.
The following steps will show us how to check for overdispersion, after which we will use a Laney U' chart:
Navigate to Stat | Control Charts | Attributes Charts and select U Chart Diagnostic….
Enter the data from the column containing the counts of events in the Variables: field.
Enter the data from the subgroup size column in the Subgroups sizes: field.
Click on OK.
Check the results of the U Chart Diagnostic… option. If the u-chart diagnostic indicates overdispersion or underdispersion, proceed to step 6. If not, use the u-chart (see the previous example).
Navigate to Stat | Control Charts | Attributes charts and select Laney U' Chart.
Enter the column containing...