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CCHART Statement |

See SHWCCHR1 in the SAS/QC Sample Library |

In the previous example, the input data set provided
the number of nonconformities per subgroup sample. However, in some
applications, as illustrated here,
the data may be provided as the number of
nonconformities *per inspection unit* for each subgroup.

A clothing manufacturer ships shirts in boxes of ten. Prior
to shipment, each shirt is inspected for flaws. Since the
manufacturer is interested in the average number of flaws per
shirt, the number of flaws found in each box is divided
by ten and then recorded. The following statements create a SAS
data set named SHIRTS, which contains the average number of
flaws per shirt for 25 boxes:

data shirts; input box avgdefu @@; avgdefn=10; datalines; 1 0.4 2 0.7 3 0.5 4 1.0 5 0.3 6 0.2 7 0.0 8 0.4 9 0.4 10 0.6 11 0.2 12 0.7 13 0.3 14 0.1 15 0.3 16 0.6 17 0.6 18 0.3 19 0.7 20 0.3 21 0.0 22 0.1 23 0.5 24 0.6 25 0.4 ;

A listing of SHIRTS is shown in Figure 33.6.

The data set SHIRTS contains three variables: the box number (BOX),
the average number of flaws per shirt (AVGDEFU), and the number
of shirts per box (AVGDEFN). Here, a *subgroup* is a box of
shirts, and an *inspection unit* is an individual shirt.
Note that each subgroup consists of ten inspection units.

To create a *c* chart plotting the total number of
flaws per box (instead of per shirt), you can
specify SHIRTS as a HISTORY= data set.

title 'Total Flaws per Box of Shirts'; symbol v=dot c=red; proc shewhart history=shirts; cchart avgdef*box / cframe = steel cconect = red cinfill = ligr coutfill = yellow ; run;

Note that AVGDEF is *not* the name of a SAS variable in the
data set but is instead the common prefix for the
SAS variable names AVGDEFU and AVGDEFN. The suffix characters
*U* and *N* indicate *number of nonconformities per
unit* and *sample size*, respectively. This naming convention
enables you to specify two variables in the HISTORY= data set with a
single name referred to as the *process*. The name BOX specified
after the asterisk is the name of the *subgroup-variable*.
The *c* chart is shown in Figure 33.7.

In general, a HISTORY= input data set used with the CCHART
statement must contain the following variables:

- subgroup variable
- subgroup number of nonconformities per unit variable
- subgroup sample size variable

Furthermore, the names of the nonconformities per
unit and sample size variables must begin with the *process*
name specified in the CCHART statement and end with the
special suffix characters *U* and *N*, respectively.
If the names do not follow this
convention, you can use the RENAME option
to rename the variables for the duration of the SHEWHART
procedure step.
Suppose that, instead of the variables AVGDEFU and
AVGDEFN, the data set SHIRTS contained the variables SHIRTDEF
and SIZES. The following statements would temporarily rename
SHIRTDEF and SIZES to AVGDEFU and AVGDEFN:

proc shewhart history=shirts (rename=(shirtdef = avgdefu sizes = avgdefn )); cchart avgdef*box; run;

For more information, see "HISTORY= Data Set" .

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