CNPK
Name:
Type:
Purpose:
Compute the process capability index (CNPK) for a variable.
Description:
The process capability index measure the performance (i.e., the
capability) of an industrial process. The CNPK is a variant of
the CPK capability indices used for nonnormal data and is
defined as:
where
where USL and LSL are user specified upper and lower specification
limits, MEDIAN is the median of the data values, and \( p_{0.995} \)
and \( p_{0.005} \) are the 99.5 and 0.5 percentiles of the data
respectively.
The specification limits define the range within which a
product is considered acceptable (values outside this range
indicate that a product is defective).
Syntax:
LET <param> = CNPK <y>
<SUBSET/EXCEPT/FOR qualification>
where <y> is the response variable;
<param> is a parameter where the computed CNPK
is stored;
and where the <SUBSET/EXCEPT/FOR qualification> is optional.
Examples:
LET A = CNPK Y1
LET A = CNPK Y1 SUBSET TAG > 2
Note:
The upper and lower specification limits must be specified by the
user as follows:
LET LSL = <value>
LET USL = <value>
Note:
Recall that Chebychev's theorem states that at least 75% of the
variables data must fall within plus or minus 2 standard
deviations of the mean and that at least 88% must fall within
plus or minus 3 standard deviations. This is for any
distribution. For a normal distribution, these numbers are
95.4% and 99.7% respectively.
Default:
Synonyms:
Related Commands:
CONTROL
CHART

= Generate a control chart.

STATISTIC
PLOT

= Generate a statistic versus subset plot.

DEX ... PLOT

= Generate a dex <statistic> plot.

CP

= Compute the process capability index.

CPK

= Compute the process capability index.

CC

= Compute the process capability index.

CPM

= Compute the process capability index.

PERCENT DEFECTIVE

= Compute the percentage of defectives in a sample.

EXPECTED LOSS

= Compute the expected loss of a sample.

Reference:
Kaoru Ishikawa (1982), "Guide to Quality Control,"
Asian Productivity Organization, (chapter 13).
Applications:
Implementation Date:
Program:
LET Y1 = NORMAL RANDOM NUMERS FOR I = 1 1 100
LET LSL = 2
LET USL = 2
LET A1 = CPNK Y1
