The I-MR-R/S uses both between-subgroup and within-subgroup variations to generate three control charts, the individuals, moving range and R or S charts. These three charts can help to assess the process level, variation between samples and variation within samples respectively. It is useful when the overall process variation is due to both between subgroup variation and random error.
1. Choose ProcessMA > Control Charts > Variable Charts for Subgroups > I-MR-R/S.
2. In Variable, select the column containing the data.
· For constant subgroup size:
- Check Constant size.
- In Subgroup, enter the subgroup size.
· For non-constant subgroup size:
- Uncheck Constant size.
- In Subgroup, select the column containing the subgroup codes.
3. Click OK.
Optional
4. In Mean, enter the population mean, otherwise it will be estimated by the sample mean.
5. In Std dev between subgroups, enter the population standard deviation, otherwise it will be estimated from the data.
6. In Std dev within subgroups, enter the population standard deviation, otherwise it will be estimated from the data.
7. In Control limit multiples, enter the position to draw the upper and lower control limits. Multiple entries must be separated by commas (,).
8. In I-Lower limit bound, enter the bound on the lower control limit for the Individuals Chart.
9. In I-Upper limit bound, enter the bound on the upper control limit for the Individuals Chart.
10. In MR-Lower limit bound, enter the bound on the lower control limit for the Moving Range Chart.
11. In MR-Upper limit bound, enter the bound on the upper control limit for the Moving Range Chart.
12. In R/S-Lower limit bound, enter the bound on the lower control limit for the R or S Chart.
13. In R/S-Upper limit bound, enter the bound on the upper control limit for the R or S Chart.
14. In Phase, select the column containing the phase codes. (Phase can useful to compare groups of data like before and after improvement)
15. In Method (Subgroup size=1), select the method of estimating sigma when subgroup size is 1.
· Average moving range – Estimate based on the average of the moving range.
· Median moving range – Estimate based on the median of the moving range
16. In Method (Subgroup size>1), select the method of estimating sigma when subgroup size is greater than 1.
· Rbar - Estimate based on the average of the subgroup ranges.
· Sbar -Estimate based on the average of the subgroup standard deviations.
· Pooled standard deviation - Estimate based on pooled standard deviation.
17. 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.
Std dev between subgroups: Numeric.
Std dev within subgroups: Numeric.
Control limit multiples: Numeric.
I-Lower limit bound: Numeric.
I-Upper limit bound: Numeric.
MR-Lower limit bound: Numeric.
MR-Upper limit bound: Numeric.
R/S-Lower limit bound: Numeric.
R/S-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 operations manager in a production plant. You need to ensure that the dimensions of the parts manufactured are in control and within specifications. You took measurements of 10 parts from each of the 8 production lines. You want to generate a I-MR-R/S Chart to monitor the process.
1. Open worksheet ProcessMA > Tools > Data Files > Control.xls.
2. Choose ProcessMA > Control Charts > Variable Charts for Subgroups > I-MR-R/S.
3. In Variable, select C – Parts.
4. In Subgroup, select D – Subgroup.
5. Click OK.
Interpretation
The process is in control within and between subgroups (production lines).