See CAPCMH1 in the SAS/QC Sample LibraryThe effective channel length (in microns) is measured for 1225 field effect transistors. The channel lengths are saved as
values of the variable Length
in a SAS data set named Channel
:
data Channel; length Lot $ 16; input Length @@; select; when (_n_ <= 425) Lot='Lot 1'; when (_n_ >= 926) Lot='Lot 3'; otherwise Lot='Lot 2'; end; datalines; 0.91 1.01 0.95 1.13 1.12 0.86 0.96 1.17 1.36 1.10 0.98 1.27 1.13 0.92 1.15 1.26 1.14 0.88 1.03 1.00 0.98 0.94 1.09 0.92 1.10 0.95 1.05 1.05 1.11 1.15 1.11 0.98 0.78 1.09 0.94 1.05 0.89 1.16 0.88 1.19 1.01 1.08 1.19 0.94 0.92 1.27 0.90 0.88 1.38 1.02 ... more lines ... 1.80 2.35 2.23 1.96 2.16 2.08 2.06 2.03 2.18 1.83 2.13 2.05 1.90 2.07 2.15 1.96 2.15 1.89 2.15 2.04 1.95 1.93 2.22 1.74 1.91 ;
The data set Channel
is also used in Example 5.12, where a kernel density estimate is superimposed on the histogram of channel lengths. The display in Output 5.12.1 reveals that there are three distinct peaks in the process distribution. To investigate whether these peaks (modes) in the
histogram are related to the lot source, you can create a comparative histogram that uses Lot
as a classification variable. The following statements create the comparative histogram shown in Figure 5.6:
ods graphics off; title "Comparative Analysis of Lot Source"; proc capability data=Channel noprint; specs lsl = 0.8 usl = 2.0; comphist Length / class = Lot nrows = 3 nlegend = 'Lot Size' nlegendpos = nw; label Lot = 'Transistor Source'; run;
The COMPHISTOGRAM statement requests a comparative histogram for the process variable Length
. The CLASS= option requests a component histogram for each level (distinct value) of the classification variable Lot
. The option NROWS=3 stacks the histograms three to a page. The NLEGEND= option adds a sample size legend to each component
histogram, and the option NLEGENDPOS=NW positions each legend in the northwest corner. The SPEC statement provides the specification
limits displayed as vertical reference lines. See the section Dictionary of Options for descriptions of these options, and see the section SPEC Statement for details of the SPEC statement.
Figure 5.6: Comparison by Lot Source