Capability Sixpack (Normal Distribution)
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Stat > Quality Tools > Capability Sixpack > Normal

Use to produce process capability report when your data follow a normal distribution.

To confirm process stability, the report includes:

·    An Xbar chart (or Individuals chart for individual observations)

·    An R chart, an S chart, or an  MR chart, depending on the size of the subgroups (see Capability Sixpack (Normal Distribution) - Estimation of Standard Deviation)

·    A run chart of the last 25 subgroups (or last 25 observations)

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

·    Within and overall capability statistics; Cp, Cpk, Cpm (if you specify a target), Pp, Ppk, or benchmark Z values (instead of Cp and Pp).

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

A model that assumes the data are from a normal distribution suits most process data. If your data are either very skewed or the within-subgroup variation is not constant (for example, when this variation is proportional to the mean), 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 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 deviation (optional): Enter a value for 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 standard deviation, it is estimated from the data. See <Estimate> for estimation options.

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