Reading Preestablished Control Limits

CCHART Statement

Reading Preestablished Control Limits

See SHWCCHR1 in the SAS/QC Sample Library

In the previous example, control limits were saved in a SAS data set named DEFLIM. This example shows how these limits can be applied to defect data for a second group of trucks, which are provided in the following data set:

   data trucks2;
      input truckid $ defects @@;
      label truckid='Truck Identification Number'
            defects='Number of Paint Defects';
      datalines;
   R1   7   R2   3   R3   3   R4  14   R5   7
   R6   9   R7   3   R8  11   S4   6   S9   8
   S7   3   S6  10   T3   9   T4   4   T7   7
   X1   7   X2  18   X3   3   X9  11   X4   5
   ;

The following statements plot the number of paint defects for the second group of trucks on a c chart using the control limits in DEFLIM. The chart is shown in Figure 33.5.

   title 'c Chart for Paint Defects in New Trucks';
   symbol v=dot c=red;
   proc shewhart data=trucks2 limits=deflim;
      cchart defects*truckid / cframe   = steel
                               cconnect = red
                               cinfill  = ligr
                               coutfill = yellow ;
   run;

Figure 33.5: A c Chart for the Second Set of Trucks

Note that the number of defects on the truck with identification number X2 exceeds the upper control limit, indicating that the process is out-of-control. The LIMITS= option in the PROC SHEWHART statement specifies the data set containing the control limits. By default,^* this information is read from the first observation in the LIMITS= data set for which

the value of _VAR_ matches the process name DEFECTS
the value of _SUBGRP_ matches the subgroup-variable name TRUCKID

In this example, the LIMITS= data set was created in a previous run of the SHEWHART procedure. You can also create a LIMITS= data set with the DATA step. See "LIMITS= Data Set" for details concerning the variables that you must provide.

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