Capability Sixpack (Between/Within) -
Estimation of Standard Deviationmain topic see also
Capability Sixpack (Between/Within) -
Estimation of Standard DeviationStat > Quality Tools > Capability Sixpack > Between/Within > Estimate
Allows you to specify the method for estimating the population standard deviation.
You can set preferences for the estimation of s using Tools > Options > Control Charts and Quality Tools > Estimating Sigma.
Whether Minitab displays an R chart or an S chart depends on the size of the subgroups. If more than 50% of the subgroups are the same size, then the most common subgroup size determines the chart. Otherwise, the largest subgroup size determines the chart. If the subgroup size is 8 or less, Minitab displays an R chart. If the subgroup size is 9 or more, Minitab displays an S chart.
Methods of estimating standard deviation
Capability Statistics
Within subgroup: Choose how to estimate the within-subgroup standard deviation for the capability statistics.
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.
Between subgroups: Choose how to estimate the between-subgroups standard deviation for the capability statistics.
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 mean squared successive differences.
Control Charts
Within subgroup: Choose how to estimate the within-subgroup standard deviation for the control charts.
(for subgroup sizes <= 8)
Rbar: Use the average of the subgroup ranges.
Pooled standard deviation: Use a pooled standard deviation.
(for subgroup sizes > 8)
Sbar: Use the average of the subgroup standard deviations.
Pooled standard deviation: Use a pooled standard deviation.
Between subgroups: Choose how to estimate the between-subgroups standard deviation for the control charts.
Average moving range: Use the average of the moving range.
Median moving range: Use the median of the moving range.
Use unbiasing constants to calculate standard deviations
Within subgroup: Check to estimate within-subgroup standard deviation using unbiasing constants.
Overall (capability statistics only): Check to estimate the overall standard deviation using unbiasing constants.
Use moving range of length: Enter the number of observations used to calculate the moving range. By default, a span of 2 is used as consecutive values have the greatest chance of being alike.