BOXCHART Statement: SHEWHART Procedure

Saving Summary Statistics

[See SHWBOXA in the SAS/QC Sample Library]In this example, the BOXCHART statement is used to create a summary data set that can be read later by the SHEWHART procedure (as in the preceding example). The following statements read measurements from the data set Turbine and create a summary data set named Turbhist:

title 'Summary Data Set for Power Output';
proc shewhart data=Turbine;
   boxchart KWatts*Day / outhistory = Turbhist
                         nochart;
run;

The OUTHISTORY= option names the output data set, and the NOCHART option suppresses the display of the chart, which would be identical to the chart in Figure 15.4.

Figure 15.8 contains a partial listing of Turbhist.

There are nine variables in the data set Turbhist.

• Day is the subgroup variable.

• KWattsL contains the subgroup minimums.

• KWatts1 contains the first quartiles for each subgroup.

• KWattsX contains the subgroup means.

• KWattsM contains the subgroup medians.

• KWatts3 contains the third quartiles for each subgroup.

• KWattsH contains the subgroup maximums.

• KWattsS contains the subgroup standard deviations.

• KWattsN contains the subgroup sample sizes.

Note that the summary statistic variables are named by adding the suffix characters L, 1, X, M, 3, H, S, and N to the process KWatts specified in the BOXCHART statement. In other words, the variable naming convention for OUTHISTORY= data sets is the same as that for HISTORY= data sets.

If you specify the RANGES option, the OUTHISTORY= data set includes a subgroup range variable, rather than a subgroup standard deviation variable, as demonstrated by the following statements:

proc shewhart data=Turbine;
   boxchart KWatts*Day / outhistory = Turbhist2
                         ranges
                         nochart;
run;

Figure 15.9 contains a partial listing of Turbhist2. The variable KWattsR contains the subgroup ranges.

The RANGES option is not recommended when the subgroup sample sizes are greater than 10, nor when you use the NOLIMITS option to create standard side-by-side box-and-whisker plots.

For more information, see OUTHISTORY= Data Set.