Capability Sixpack (Between/Within)
overview     data     how to     example     see also  

Stat > Quality Tools > Capability Sixpack > Between/Within

Use to produce process capability report when your data follow a normal distribution. Use this feature when you suspect that you may have both between-subgroup and within-subgroup variation.

To confirm process stability, the report includes:

·    An individuals chart of subgroup means

·    A moving range chart of subgroup means

·    An R chart or S chart, depending on the size of the subgroups (see Capability Sixpack (Between/Within) - Estimation of Standard Deviation)

To confirm normality, the report includes:

·    A histogram of the process data

·    A normal probability plot (with 95% confidence interval, Anderson-Darling, and p-values)

To assess capability, the report includes:

·    A process capability plot

·    Between/within and overall capability statistics; Cp, Cpk, Cpm (if you specify a target), Pp, and Ppk

You can also use this feature to correct nonnormality in your data using a Box-Cox transformation, then perform capability on the transformed data.

A model that assumes that the data are from a normal distribution suits most process data. If your data are very skewed, see Nonnormal data.

Dialog box items

Data are arranged as

Single column: Choose if data is in one column. Enter a column.

Subgroup size (use a constant or an ID column): Enter the subgroup size (for equal-size subgroups) or a column of subscripts (for unequal-size subgroups). If the subgroups are not equal, the control limits on the R chart or S chart will not be straight lines but will vary with the subgroup size.

Subgroups across rows of: Choose if subgroups are arranged in rows across several columns. Enter the columns.

Lower spec: Enter the lower specification limit.

Upper spec: Enter the upper specification limit.

Historical mean (optional): Enter a value for the mean of the population distribution if you have a known process parameter or an estimate obtained from past data. If you do not specify a value for the mean, it is estimated from the data.

Historical Standard Deviations

Within subgroup: (optional): Enter a value for the within-subgroup standard deviation of the population distribution if you have a known process parameter or an estimate obtained from past data. If you do not specify a value for sigma, it is estimated from the data.

Between subgroups: (optional): Enter a value for the between-subgroup standard deviation of the population distribution if you have a known process parameter or an estimate obtained from past data. If you do not specify a value for sigma, it is estimated from the data.

<Box-Cox>

<Tests>

<Estimate>

<Options>