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UCHART Statement |

See SHWUCHR in the SAS/QC Sample Library |

In the previous example,
the input data set
provided the number of nonconformities for each
subgroup sample. However, in some
applications, as illustrated here, the data provide 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 ;

Note that this is the same data set used in "Getting Started" of Chapter 33, "CCHART Statement." A listing of SHIRTS is shown in Figure 41.6.

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 contains ten inspection units.

To create a *u* chart for the average number
of flaws per shirt in each box, you can specify
SHIRTS as a HISTORY= data set.

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

Note that AVGDEF is *not* the name of a SAS variable in the
data set but is, instead, the common prefix for
the names of the
SAS variables 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, which is referred to as the *process*.
The name BOX, specified after the asterisk, is the name of the
*subgroup-variable*.
The *u* chart is shown in Figure 41.7.

In general, a HISTORY= input data set used with the UCHART
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 UCHART 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 temporarily rename SHIRTDEF
and SIZES to AVGDEFU and AVGDEFN:

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

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

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