Non-parametric capability analysis

This macro calculates capability indices (Cnpk) using the empirical percentile method as described in the reference D. W. McCormack Jr., Ian R. Harris, Arnon M. Hurwitz, and Patrick D. Spagon 2000). "Capability Indices for Non-Normal Data," Quality Engineering, 12 (4), 489-495. There are other nonparametric capability analysis methods available. Only the empirical percentile method is shown here.

Typically you would only use this method when your data does not follow the normal distribution or any of the other distributions that can be used in a capability analysis in Minitab. The author of this macro strongly suggests that you use Stat > Quality Tools > Individual Distribution Identification to determine if your data follows any of the distributions listed. These distributions are normal, lognormal, 3-parameter lognormal, exponential, 2-parameter exponential, Weibull, 3-parameter Weibull, largest extreme value, smallest extreme value, gamma, 3-parameter gamma, logistic, loglogistic, and 3-parameter loglogistic.

Download the Macro

Be sure that Minitab knows where to find your downloaded macro. Choose Tools > Options > General. Under Macro location browse to the location where you save macro files.


If you use an older web browser, when you click the Download button, the file may open in Quicktime, which shares the .mac file extension with Minitab macros. To save the macro, right-click the Download button and choose Save target as.

Required Inputs

  • A column of at least 100 numeric observations

Optional Inputs

Use to specify your lower specification limit.
Use to specify your upper specification limit.

Running the Macro

Suppose your data is in C2 and you have a lower spec limit (LSL) of 12 and an upper spec limit (USL) of 16.To run the macro, choose Edit > Command Line Editor and type:

LSL 12; 
USL 16.

Click Submit Commands.

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