with \( P(x) \), ENGLSL and ENGUSL denoting the percentile function,
lower engineering specification limit and the upper engineering
specification limit, respectively. This statistic has coverage
comparable to the normal-based C_{p} statistic for
\( \pm 3 \sigma \). An alternative definition has 99% coverage and
is defined as
This is a non-parametric alternative to the normal-based
C_{p} process capability index.
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 <par> = CNP <y>
<SUBSET/EXCEPT/FOR qualification>
where <y> is the response variable;
<par> is a parameter where the computed C_{np}
is stored;
and where the <SUBSET/EXCEPT/FOR qualification> is optional.
Examples:
LET A = CNP Y1
LET A = CNP 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:
To use the alternative definition, enter the command
SET CNPK DEFINITION AIRFORCE
To reset the default, enter
SET CNPK DEFINITION PEARN
Note:
Dataplot statistics can be used in a number of commands. For
details, enter
Kotz and Johnson (1993), "Process Capability Indices,"
Chapman & Hall (chapter 2).
Chen and Ding (2001), "A New Process Capability Index for Non-Normal
Distributions," International Journal of Quality & Reliability
Management, Vol. 18, No. 7, pp. 762-770.
Applications:
Quality Control
Implementation Date:
2015/04
Program:
SKIP 25
READ FURNACE.DAT X1 X2 X3 Y
LET LSL = 460
LET USL = 660
LET A = CNP Y
MULTIPLOT CORNER COORDINATES 5 5 95 95
MULTIPLOT 2 2
MULTIPLOT SCALE FACTOR 2
TITLE AUTOMATIC
CNP PLOT Y X1
CNP PLOT Y X2
CNP PLOT Y X3
END OF MULTIPLOT
Date created: 07/31/2023
Last updated: 07/31/2023
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