with \( P(x) \), TARGET, ENGLSL, ENGUSL and \( \tilde{x} \) denoting
the percentile function, the target engineering limit, the lower
engineering specification limit, the upper engineering specification
limit and the sample median, respectively. This statistic has coverage
comparable to the normal-based C_{pm} statistic for
\( \pm 3 \sigma \). An alternative definition has 99% coverage and
uses P(0.995) and P(0.005) in the above formula.
This statistic is a non-parametric alternative to the normal-based
C_{pm} 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> = CNPM <y>
<SUBSET/EXCEPT/FOR qualification>
where <y> is the response variable;
<par> is a parameter where the computed CNPM is
stored;
and where the <SUBSET/EXCEPT/FOR qualification> is optional.
Examples:
LET A = CNPM Y1
LET A = CNPM Y1 SUBSET TAG > 2
Note:
The upper and lower specification limits must be specified by the
user as follows:
LET TARGET = <value>
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
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.
Kaoru Ishikawa (1982), "Guide to Quality Control,"
Asian Productivity Organization, (chapter 13).
Applications:
Quality Control
Implementation Date:
2015/04
Program:
SKIP 25
READ FURNACE.DAT X1 X2 X3 Y
LET TARGET = 550
LET LSL = 460
LET USL = 660
LET A = CNPM Y
MULTIPLOT CORNER COORDINATES 5 5 95 95
MULTIPLOT 2 2
MULTIPLOT SCALE FACTOR 2
TITLE AUTOMATIC
CNPM PLOT Y X1
CNPM PLOT Y X2
CNPM PLOT Y X3
END OF MULTIPLOT
Date created: 07/31/2023
Last updated: 07/31/2023
Please email comments on this WWW page to
alan.heckert@nist.gov.