This example illustrates how to create a comparative histogram. The effective channel length (in microns) is measured for
1225 field effect transistors. The channel lengths (Length
) are stored in a data set named Channel
, which is partially listed in Output 4.15.1:
Output 4.15.1: Partial Listing of Data Set Channel
The Data Set Channel |
Lot | Length |
---|---|
Lot 1 | 0.91 |
. | . |
Lot 1 | 1.17 |
Lot 2 | 1.47 |
. | . |
Lot 2 | 1.39 |
Lot 3 | 2.04 |
. | . |
Lot 3 | 1.91 |
The following statements request a histogram of Length
ignoring the lot source:
title 'Histogram of Length Ignoring Lot Source'; ods graphics off; proc univariate data=Channel noprint; histogram Length; run;
The resulting histogram is shown in Output 4.15.2.
Output 4.15.2: Histogram for Length Ignoring Lot Source
To investigate whether the peaks (modes) in Output 4.15.2 are related to the lot source, you can create a comparative histogram by using Lot
as a classification variable. The following statements create the histogram shown in Output 4.15.3:
title 'Comparative Analysis of Lot Source'; ods graphics off; proc univariate data=Channel noprint; class Lot; histogram Length / nrows = 3; run;
The CLASS statement requests comparisons for each level (distinct value) of the classification variable Lot
. The HISTOGRAM statement requests a comparative histogram for the variable Length
. The NROWS= option specifies the number of rows per panel in the comparative histogram. By default, comparative histograms
are displayed in two rows per panel.
Output 4.15.3: Comparison by Lot Source
Output 4.15.3 reveals that the distributions of Length
are similarly distributed except for shifts in mean.
A sample program for this example, uniex09.sas, is available in the SAS Sample Library for Base SAS software.