Capability Analysis (Nonnormal Distribution)
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Stat > Quality Tools > Capability Analysis > Nonnormal

Use to produce a process capability report when your data do not follow a nonnormal distribution.. The report includes a capability histogram overlaid with a distribution curve, and a table of overall capability statistics. The report also includes statistics of the process data, such as the mean, distribution parameter estimates, target (if you enter one), and process specifications; the actual overall capability (Pp, Ppk, PPU, and PPL), and the observed and expected overall performance. Minitab bases the calculations on maximum likelihood estimates of the distribution parameters, rather than mean and variance estimates as in the normal case. You can use the report to visually assess the distribution of the process relative to the target, whether the data follow a specified distribution, and whether the process is capable of meeting the specifications consistently.

Minitab features two options for calculating overall capability indices for nonnormal data: the ISO method and the Minitab method. The ISO method is the default. To change the selection, see: Tools > Options > Control Charts and Quality Tools > Capability Analysis.

Dialog box items

Data are arranged as

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

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

Fit distribution: Choose a distribution that fits your data. See Individual Distribution Identification if you are unsure which distribution adequately fits your data.

Lower spec: Enter a lower specification limit. Check Boundary to define the number as a "hard" limit, meaning that it is impossible for a measurement to fall outside the limit.

Upper spec: Enter an upper specification limit. Check Boundary to define the number as a "hard" limit, meaning that it is impossible for a measurement to fall outside the limit.

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