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| The UNIVARIATE Procedure |
Example 4.5 Creating Plots for Line Printer Output
The PLOT option in the PROC UNIVARIATE statement requests several basic plots for display in line printer output. For more information about plots created by the PLOT option, see the section Creating Line Printer Plots. This example illustrates the use of the PLOT option as well as BY processing in PROC UNIVARIATE.
A researcher is analyzing a data set consisting of air pollution data from three different measurement sites. The data set AirPoll, created by the following statements, contains the variables Site and Ozone, which are the site number and ozone level, respectively.
data AirPoll (keep = Site Ozone);
label Site = 'Site Number'
Ozone = 'Ozone level (in ppb)';
do i = 1 to 3;
input Site @@;
do j = 1 to 15;
input Ozone @@;
output;
end;
end;
datalines;
102 4 6 3 4 7 8 2 3 4 1 3 8 9 5 6
134 5 3 6 2 1 2 4 3 2 4 6 4 6 3 1
137 8 9 7 8 6 7 6 7 9 8 9 8 7 8 5
;
run;
The following statements produce stem-and-leaf plots, box plots, and normal probability plots for each site in the AirPoll data set:
ods select Plots SSPlots; proc univariate data=AirPoll plot; by Site; var Ozone; run;
The PLOT option produces a stem-and-leaf plot, a box plot, and a normal probability plot for the Ozone variable at each site. Because the BY statement is used, a side-by-side box plot is also created to compare the ozone levels across sites. Note that AirPoll is sorted by Site; in general, the data set should be sorted by the BY variable by using the SORT procedure. The ODS SELECT statement restricts the output to the "Plots" and "SSPlots" tables; see the section ODS Table Names. Optionally, you can specify the PLOTSIZE=
option to control the approximate number of rows (between 8 and the page size) that the plots occupy.
Output 4.5.1 through Output 4.5.3 show the plots produced for each BY group. Output 4.5.4 shows the side-by-side box plot for comparing Ozone values across sites.
Stem Leaf # Boxplot
9 0 1 |
8 00 2 |
7 0 1 +-----+
6 00 2 | |
5 0 1 | |
4 000 3 *--+--*
3 000 3 +-----+
2 0 1 |
1 0 1 |
----+----+----+----+
Normal Probability Plot
9.5+ *++++
| * * ++++
| * +++++
| * *+++
5.5+ +*++
| **+*
| * *+*+
| *++++
1.5+ *++++
+----+----+----+----+----+----+----+----+----+----+
-2 -1 0 +1 +2
|
Stem Leaf # Boxplot
6 000 3 |
5 0 1 +-----+
4 000 3 | |
3 000 3 *--+--*
2 000 3 +-----+
1 00 2 |
----+----+----+----+
Normal Probability Plot
6.5+ * * ++*+++
| * ++++++
| **+*+++
| **+*+++
| *+*+*++
1.5+ * ++*+++
+----+----+----+----+----+----+----+----+----+----+
-2 -1 0 +1 +2
|
Stem Leaf # Boxplot
9 000 3 |
8 00000 5 +-----+
7 0000 4 +--+--+
6 00 2 |
5 0 1 0
----+----+----+----+
Normal Probability Plot
9.5+ * *++++*++++
| * ** *+*+++++
7.5+ * * **++++++
| *++*+++++
5.5+ +++*++++
+----+----+----+----+----+----+----+----+----+----+
-2 -1 0 +1 +2
|
|
10 +
|
| | |
| | |
8 + | *-----*
| | | + |
| +-----+ +-----+
| | | |
6 + | | | |
| | | |
| | + | +-----+ 0
| | | | |
4 + *-----* | |
| | | | + |
| +-----+ *-----*
| | | |
2 + | +-----+
| | |
| | |
|
0 +
------------+-----------+-----------+-----------
Site 102 134 137
|
Note that you can use the PROBPLOT statement with the NORMAL option to produce high-resolution normal probability plots; see the section Modeling a Data Distribution.
Note that you can use the BOXPLOT procedure to produce box plots that use high-resolution graphics. See Chapter 24, The BOXPLOT Procedure (SAS/STAT 9.22 User's Guide).
A sample program for this example, uniex04.sas, is available in the SAS Sample Library for Base SAS software.
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