Dataplot

Vol 1

Auxiliary Chapter

CC

CC (LET)

Let Subcommand

Compute the process capability index (CC) for a variable.

The process capability index measure the performance (i.e., the capability) of an industrial process. The CC is a variant of the CP and CPK capability indices.

where USL and LSL are user specified upper and lower specification limits, TARGET is the target engineering limit, is the sample mean of the data. For this statistic, smaller is better.

The specification limits define the range within which a product is considered acceptable (values outside this range indicate that a product is defective).

LET <par> = CC <y>             <SUBSET/EXCEPT/FOR qualification>
where <y> is the response variable;
            <par> is a parameter where the computed CC is stored;
and where the <SUBSET/EXCEPT/FOR qualification> is optional.

LET A = CC Y1
LET A = CC Y1 SUBSET TAG > 2

The upper and lower specification limits and target value must be specified by the user as follows:
LET LSL = <value>
LET USL = <value>
LET TARGET = <value>

This statistic is also supported for the following plots:
CC PLOT Y X
DEX CC PLOT Y X1 ... Xk


You need to specify the LSL, USL, and TARGET values (see above) before entering these commands. For more information on these plots, enter

HELP STATISTIC PLOT
HELP DEX PLOT

None

None

CONTROL CHART	= Generate a control chart.
STATISTIC PLOT	= Generate a statistic versus subset plot.
DEX PLOT	= Generate a dex plot.
CP (LET)	= Compute the process capability index.
CPK (LET)	= Compute the process capability index.
CPNK (LET)	= Compute the process capability index.
CPM (LET)	= Compute the process capability index.
PERCENT DEFECTIVE (LET)	= Compute the percentage of defectives in a sample.
EXPECTED LOSS (LET)	= Compute the expected loss of a sample.

"Guide to Quality Control", Kaoru Ishikawa, Asian Productivity Organization, 1982 (chapter 13).

Quality Control

1998/12

SKIP 25
READ GEAR.DAT Y X
LET USL = 0.995
LET USL = 1.005
LET TARGET = 1.0
CHARACTER X BLANK
LINE BLANK SOLID
TITLE AUTOMATIC
XTIC OFFSET 0.5 0.5
TIC OFFSET UNITS DATA
CC PLOT Y X