The Individuals Chart is a control chart of individual observations. It is used to track the process level and detect signs of special causes when subgroup size is equals to 1.
1. Choose ProcessMA > Control Charts > Variable Charts for Individuals > Individuals.
2. In Variable, select the column containing the data.
3. Click OK.
Optional
4. In Mean, enter the population mean, otherwise it will be estimated by the sample mean.
5. In Standard deviation, enter the population standard deviation, otherwise it will be estimated from the data.
6. In Control limit multiples, enter the position to draw the upper and lower control limits. Multiple entries must be separated by commas (,).
7. In Lower limit bound, enter the bound on the lower control limit.
8. In Upper limit bound, enter the bound on the upper control limit.
9. In Phase, select the column containing the phase codes. (Phase can useful to compare groups of data like before and after improvement)
10. In Estimate, select the method of estimating sigma.
· Average moving range – Estimate based on the average of the moving range.
· Median moving range – Estimate based on the median of the moving range
11. In Moving range length, enter the number of observations used to calculate the moving range.
Note To select a column of data into a textbox, double-click on any of the column names shown in the list on the left of the dialog box while in the textbox.
Variable: Numeric.
Subgroup (For non-constant subgroup size): Text or Numeric; Must contain equal number of data points as the Variable.
Subgroup (For constant subgroup size): Integer; Must be at least 2.
Mean: Numeric.
Standard deviation: Numeric.
Control limit multiples: Numeric.
Lower limit bound: Numeric.
Upper limit bound: Numeric.
Moving range length: Integer.
Phase: Text or Numeric; Must contain equal number of data points as the Variable.
You are the manager of a technical help division. There have been complains that response time were getting slow and erratic. You collected several measurements on response time and you want to run the I-MR Chart to evaluate the situation.
1. Open worksheet ProcessMA > Tools > Data Files > Control.xls.
2. Choose ProcessMA > Control Charts > Variable Charts for Individuals > Individuals.
3. In Variable, select F – Response time.
4. In Lower limit bound, enter 0.
5. Click OK.
Interpretation
The ninth point lies outside the upper control limit which suggests a possible special cause. Further investigation is required and it is possible that it is the cause of that complaint.