How Do I Create I-MR-R/S Control Charts in Excel Using SigmaXL?
I-MR-R ChartsIf the within-subgroup variability is much smaller than between subgroup, the classical X-bar & R (or S) chart will not work, producing numerous (false) alarms. The correct chart to use, in this case, is the I-MR-R (or S) chart. The subgroup averages are treated as individual values (I-MR) and the within subgroup ranges are plotted on the Range chart.
- Open Multi-Vari Data.xls. Select Sheet Between. We saw this data previously using Multi-Vari charts. First, we will incorrectly use the X-bar & R chart, and then apply the correct I-MR-R chart.
- Click SigmaXL > Control Charts > X-bar & R. Check Use Entire Data Table.
- Click Next. Select
Stacked Column Format. Select Measurement, click
Numeric Data Variable (Y) >>; select unit, click
Subgroup Column or Size >>.
- Click OK. Resulting X-bar & R chart:
- Almost all of the data points in the X-bar chart are out-of-control! This is due to the small within-subgroup variability (the control limits are calculated from the within-subgroup variability).
- Click Sheet Between. Select SigmaXL > Control Charts > Advanced Charts > I-MR-R.
Next. Select Stacked Column Format. Select
Measurement, click Numeric Data Variable (Y) >>; select
unit, click Subgroup Column or Size >>.
OK. Resulting I-MR-R chart:
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