Writing a SAS program: the PROC Step
The next step is to create PROC (procedure) steps. SAS procedures read the SAS data and perform various computations and print the results of these computations. The FREQ procedure computes the frequencies on specified variables; the TTEST procedure performs a t-test analysis on the specified variables. In short, the statements that ask SAS to process or analyze a specified data set are known as PROC steps. The DATA steps and PROC steps can be used in any order within a SAS program. As the DATA step starts with a DATA statement the PROC step starts with a PROC statement.
VAR var1 var2;
This procedure requests SAS to print data values for variables 1 and 2. If the VAR statement is omitted data values for each variable in the data set will be printed. DATA=dataname is an optional statement. If this is omitted SAS selects the most recently created data set within the program. It is a good practice to specify the dataname along with the PROC statement. Replace the dataname with the name of the data created in the DATA step. Printing out a few variables before doing any analysis is a good way to check whether the data are being read by SAS as you want them to be read.
FREQ Statement
TABLES var1 var2 var1*var2;
This statement produces tables showing distribution of variable values. In the above example SAS will display variable values for var1 and var2, and the combined frequency distributions for var1 and var2. For example, if you wanted to get the gender breakdown for the test scores discussed previously, you would use the following command:
TABLES sex;
The output generated by this command would look like this:
Cumulative Cumulative
SEX Frequency Percent Frequency Percent
-------------------------------------------------
f 5 50.0 5 50.0
m 5 50.0 10 100.0
MEANS Statement
VAR var1 var2;
This statement computes descriptive statistics for specified variables. If the VAR statement is omitted, descriptive statistics for each variable in the data set will be calculated.
Again, referring back to the grades data, if you wanted to generate some basic descriptive statistics for the students' test scores, the commands and output would look like this:
VAR test1 test2 test3;
The SAS System 10:00 Thursday, November 2, 1995
Variable N Mean Std Dev Minimum Maximum
--------------------------------------------------------------------
TEST1 10 80.1000000 10.4504120 60.0000000 90.0000000
TEST2 10 82.6000000 8.4616783 72.0000000 96.0000000
TEST3 10 81.2000000 10.6854002 64.0000000 93.0000000
--------------------------------------------------------------------
CORR Statement
VAR var1 var2;
A correlation analysis is performed to quantify the strength of association between two numeric variables. For example, if you wanted to see if there were a correlation between student test scores, the commands and output would look like this:
VAR test1 test2 test3;
Correlation Analysis
Pearson Correlation Coefficients / Prob > |R| under Ho: Rho=0 / N = 10
TEST1 TEST2 TEST3
TEST1 1.00000 0.75692 0.91522
0.0 0.0113 0.0002
TEST2 0.75692 1.00000 0.86857
0.0113 0.0 0.0011
TEST3 0.91522 0.86857 1.00000
0.0002 0.0011 0.0
ENDSAS statement
By this statement you indicate that there are no more data steps or procedure steps to be read or processed. ENDSAS should be followed by a semicolon (e.g., ENDSAS;). ENDSAS exist the SAS system and returns you to the UNIX environment.
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