Tools > Options > Control Charts and Quality Tools > Estimating Standard Deviation
Specify the default methods to estimate σ for various types of control charts, capability analyses, and Capability Sixpack. The changes you make to the defaults remain until you change them again, even after you exit Minitab.
Select the default method for estimating σ in R charts. This method is also used for other control charts, such as Xbar charts, when they are shown in the same graph as an R chart.
Rbar
Use the average of the subgroup ranges.
Pooled standard deviation
Use a pooled standard deviation.
S and Xbar-S Charts
Select the default method for estimating σ on S charts. This method is also used for other control charts, such as Xbar charts, when they are shown in the same graph as an S chart.
Sbar
Use the average of the subgroup standard deviations.
Pooled standard deviation
Use a pooled standard deviation.
Charts that Contain MR Charts
Select the default method for estimating σ on MR charts. This method is also used for other control charts, such as individuals charts, when they are shown in the same graph as an MR chart.
Average moving range
Use the average of the moving range.
Median moving range
Use the median of the moving range.
All Other Cases
Specify default settings for capability indices and control charts that are not listed in R and Xbar-R Charts, S and Xbar-S Charts, and Charts that Contain MR Charts.
Method for Subgroup Size > 1
Rbar
Use the average of the subgroup ranges.
Sbar
Use the average of the subgroup standard deviations.
Pooled standard deviation
Use a pooled standard deviation.
Method for Subgroup Size = 1
Average moving range
Use the average of the moving range.
Median moving range
Use the median of the moving range.
Square root of MSSD
Use the square root of MSSD (mean of the squared successive differences).
R/S Chart in I-MR-R/S Chart and Control Charts in Capability Sixpacks
Select the default method for estimating σ for an R/S chart in an I-MR-R/S chart and for control charts in Capability Sixpacks.
Method for 1 < Subgroup Size ≤ 8
Rbar
Use the average of the subgroup ranges.
Sbar
Use the average of the subgroup standard deviations.
Pooled standard deviation
Use a pooled standard deviation.
Method for Subgroup Size > 8
Sbar
Use the average of the subgroup standard deviations.
Pooled standard deviation
Use a pooled standard deviation.
All Cases
Specify default settings for using unbiasing constants and for the length of the moving range in control charts.
Use unbiasing constants to calculate standard deviations
Within subgroup
Use an unbiasing constant to calculate the within-subgroup standard deviation.
Overall (capability analysis only)
Use an unbiasing constant to calculate the overall standard deviation
Length of moving range
Specify the number of observations that are used to calculate the moving range. The default value is 2, because consecutive values have the highest chance of being alike.
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