Example 44.2: Computing Subgroup Summary Statistics

XSCHART Statement

Example 44.2: Computing Subgroup Summary Statistics

See SHWXS3 in the SAS/QC Sample Library

You can use output data sets from a number of SAS procedures as input data sets for the SHEWHART procedure. In this example, the MEANS procedure is used to create a data set containing subgroup summary statistics, which can be read by the SHEWHART procedure as a HISTORY= data set. The following statements create an output data set named OILSUMM, which contains subgroup means, standard deviations, and sample sizes for the variable KWATTS in the data set TURBINE (see "Creating Charts for Means and Standard Deviations from Raw Data" ):

   proc means data=turbine noprint;
     var kwatts;
     by day;
     output out=oilsumm mean=means std=stds n=sizes;
   run;

A listing of OILSUMM is shown in Output 44.2.1.

Output 44.2.1: The Data Set OILSUMM

Summary Statistics for Power Output Data

day	kwattsx	kwattss	kwattsn
04JUL	3487.40	220.260	20
05JUL	3471.65	210.427	20
06JUL	3488.30	147.025	20
07JUL	3434.20	157.637	20
08JUL	3475.80	258.949	20
09JUL	3518.10	211.566	20
10JUL	3492.65	193.779	20
11JUL	3496.40	212.024	20
12JUL	3398.50	199.201	20
13JUL	3456.05	173.455	20
14JUL	3493.60	187.465	20
15JUL	3563.30	205.472	20
16JUL	3519.05	173.676	20
17JUL	3474.20	200.576	20
18JUL	3443.60	222.084	20
19JUL	3586.35	185.724	20
20JUL	3486.45	223.474	20
21JUL	3492.90	145.267	20
22JUL	3432.80	190.994	20
23JUL	3496.90	208.858	20

The variables MEANS, STDS, and SIZES do not follow the naming convention required for HISTORY= data sets (see "HISTORY= Data Set" ). The following statements temporarily rename these variables to KWATTSX, KWATTSS, and KWATTSN, respectively (the names required when the process KWATTS is specified in the XSCHART statement):

   title 'Mean and Standard Deviation Charts for Power Output';
   symbol v=dot;
   proc shewhart
      history=oilsumm (rename=(means  = kwattsx
                               stds   = kwattss
                               sizes  = kwattsn ));
     xschart kwatts*day;
  run;

The resulting charts are identical to the charts in Figure 44.2.

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