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 useto 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.
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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, chooseand type:
%ECAPA C2; LSL 12; USL 16.
Click Submit Commands.