Reading Preestablished Control Limit Parameters

EWMACHART Statement

Reading Preestablished Control Limit Parameters

See MACEW1 in the SAS/QC Sample Library

In the previous example, the OUTLIMITS= data set saved the control limit parameters in the data set CLIPLIM. This example shows how to apply these parameters to new data provided in the following data set:

   data clips1a;
      label gap='Gap Measurement (mm)';
      input day @;
      do i=1 to 5;
         input gap @;
         output;
         end;
      drop i;
   datalines;
   21  14.86 15.01 14.67 14.67 15.07
   22  14.93 14.53 15.07 15.10 14.98
   23  15.27 14.90 15.12 15.10 14.80
   24  15.02 15.21 14.93 15.11 15.20
   25  14.90 14.81 15.26 14.57 14.94
   26  14.78 15.29 15.13 14.62 14.54
   27  14.78 15.15 14.61 14.92 15.07
   28  14.92 15.31 14.82 14.74 15.26
   29  15.11 15.04 14.61 15.09 14.68
   30  15.00 15.04 14.36 15.20 14.65
   31  14.99 14.76 15.18 15.04 14.82
   32  14.90 14.78 15.19 15.06 15.06
   33  14.95 15.10 14.86 15.27 15.22
   34  15.03 14.71 14.75 14.99 15.02
   35  15.38 14.94 14.68 14.77 14.83
   36  14.95 15.43 14.87 14.90 15.34
   37  15.18 14.94 15.32 14.74 15.29
   38  14.91 15.15 15.06 14.78 15.42
   39  15.34 15.34 15.41 15.36 14.96
   40  15.12 14.75 15.05 14.70 14.74
   ;

The following statements create an EWMA chart for the data in CLIPS1A using the control limit parameters in CLIPLIM:

   title 'EWMA Chart for Second Set of Gap Measurements';
   symbol v=dot c=salmon;
   proc macontrol data=clips1a limits=cliplim;
      ewmachart gap*day / cframe   = vibg
                          cinfill  = ligr
                          coutfill = yellow
                          cconnect = salmon;
   run;

The chart is shown in Figure 20.8.

The LIMITS= option in the PROC MACONTROL statement specifies the data set containing the control limit parameters. 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 GAP
the value of _SUBGRP_ matches the subgroup-variable name DAY

Figure 20.8: EWMA Chart Using Preestablished Control Limit Parameters

Note that the EWMA plotted for the 39^th day lies above the upper control limit, signalling an out-of-control process.

In this example, the LIMITS= data set was created in a previous run of the MACONTROL 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, and see Example 20.1 for an illustration.

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