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This module will illustrate the general syntax of SAS procedures. We will use the auto data file shown below to illustrate the syntax of SAS procedures.
DATA auto ; input MAKE $ PRICE MPG REP78 FOREIGN ; DATALINES; AMC 4099 22 3 0 AMC 4749 17 3 0 AMC 3799 22 3 0 Audi 9690 17 5 1 Audi 6295 23 3 1 BMW 9735 25 4 1 Buick 4816 20 3 0 Buick 7827 15 4 0 Buick 5788 18 3 0 Buick 4453 26 3 0 Buick 5189 20 3 0 Buick 10372 16 3 0 Buick 4082 19 3 0 Cad. 11385 14 3 0 Cad. 14500 14 2 0 Cad. 15906 21 3 0 Chev. 3299 29 3 0 Chev. 5705 16 4 0 Chev. 4504 22 3 0 Chev. 5104 22 2 0 Chev. 3667 24 2 0 Chev. 3955 19 3 0 Datsun 6229 23 4 1 Datsun 4589 35 5 1 Datsun 5079 24 4 1 Datsun 8129 21 4 1 ; RUN;
Now, lets have a look at the use of SAS procedures using proc means as an example. Here we show that it is possible to use proc means with no options at all. By default, it uses the last data file created (i.e., auto) and it makes means for all of the numeric variables in the file.
PROC MEANS ; RUN;
Here you see the results, the means from auto and it displays the N, mean, Std Dev, Min and Max for all of the numeric variables.
Variable N Mean Std Dev Minimum Maximum ------------------------------------------------------------------------------ PRICE 26 6651.73 3371.12 3299.00 15906.00 MPG 26 20.9230769 4.7575042 14.0000000 35.0000000 REP78 26 3.2692308 0.7775702 2.0000000 5.0000000 FOREIGN 26 0.2692308 0.4523443 0 1.0000000 ------------------------------------------------------------------------------
We can use the data= option to tell proc means for what file we want the means. The data= option comes right after proc means. Even though the data= option is optional, we strongly recommend using it every time because it avoids errors of omission when you revise your programs.
PROC MEANS DATA=auto; RUN;
As you see, the results are identical to those above.
Variable N Mean Std Dev Minimum Maximum ------------------------------------------------------------------------------ PRICE 26 6651.73 3371.12 3299.00 15906.00 MPG 26 20.9230769 4.7575042 14.0000000 35.0000000 REP78 26 3.2692308 0.7775702 2.0000000 5.0000000 FOREIGN 26 0.2692308 0.4523443 0 1.0000000 ------------------------------------------------------------------------------
We can use the n, mean and std options to tell proc means that we just want the N, mean and standard deviation for the data.
PROC MEANS DATA=auto N MEAN STD ; RUN;
The output, shown below, shows just the N, mean, and standard deviation, just as we requested.
Variable N Mean Std Dev ---------------------------------------------- PRICE 26 6651.73 3371.12 MPG 26 20.9230769 4.7575042 REP78 26 3.2692308 0.7775702 FOREIGN 26 0.2692308 0.4523443 ----------------------------------------------
These examples have shown us that you can have options on the proc statement, for example after proc means we used the data= n mean and std options.
Proc means also supports additional statements. Here we use the var statement to say which variables we want the means for proc means.
PROC MEANS DATA=auto; VAR price ; RUN;
As you would expect, the output shows the results just for the variable price.
Analysis Variable : PRICEN Mean Std Dev Minimum Maximum ------------------------------------------------------------------ 26 6651.73 3371.12 3299.00 15906.00 ------------------------------------------------------------------
Here we also use the class statement to request means broken down by foreign (i.e., foreign and domestic cars).
PROC MEANS DATA=auto; CLASS foreign ; VAR price ; RUN;
As we requested, the means of price are shown for the two levels of foreign.
Analysis Variable : PRICEN FOREIGN Obs N Mean Std Dev Minimum Maximum ----------------------------------------------------------------------------- 0 19 19 6484.16 3768.46 3299.00 15906.001 7 7 7106.57 2101.83 4589.00 9735.00 -----------------------------------------------------------------------------
These examples have shown that you can have additional statements with a proc (for example, the var and class statement). Each proc has its own set of additional statements that are valid for that proc.
It is also possible to have options on the additional statements (the statements after the proc statement). We will illustrate this using proc reg.
Here we use proc reg to predict price from mpg. We use the model statement to tell proc reg that we want to predict price from mpg.
PROC REG DATA=auto ; MODEL price = mpg ; RUN; QUIT;
Here is the output from the proc reg.
Model: MODEL1
Dependent Variable: PRICE
Analysis of Variance
Sum of Mean
Source DF Squares Square F Value Prob>F
Model 1 54620027.581 54620027.581 5.712 0.0251
Error 24 229491191.53 9562132.9806
C Total 25 284111219.12
Root MSE 3092.26988 R-square 0.1922
Dep Mean 6651.73077 Adj R-sq 0.1586
C.V. 46.48820
Parameter Estimates
Parameter Standard T for H0:
Variable DF Estimate Error Parameter=0 Prob > |T|
INTERCEP 1 13152 2786.6930753 4.720 0.0001
MPG 1 -310.689641 129.99546608 -2.390 0.0251
Notice that we don't get standardized estimates (betas). We have to ask proc reg to give those to us. In particular, we use the stb option on the model statement, as shown below. Note that the stb option comes after a / . Options on a proc statement come right after the name of the proc, but options for subsequent statements must follow a slash / .
PROC REG DATA=auto ; MODEL price = mpg / STB; RUN;
The output is the same as the output above, except that it also includes this portion shown below that has the standardized estimates (betas).
Standardized Variable DF Estimate INTERCEP 1 0.00000000 MPG 1 -0.43846180
We have illustrated the general syntax of SAS procedures using proc means and proc reg. Let's look at a few more examples, this time using proc freq. As you may imagine, proc freq is used for generating frequency tables. From what we have learned, we would expect that proc freq would have:
- Options on the proc freq statement that would influence the way that the tables look.
- Additional statements that would specify what tables to produce.
- Options on the additional statements that would influence how those particular tables look.
Let's look at some examples.
First, consider the program below. As you might expect, the program above would generate frequency tables for every variable in the auto data file.
PROC FREQ DATA=auto; RUN;
If we use the page option, proc freq will start every table on a new page. Note that this influences all of the tables produced in that proc freq step.
PROC FREQ DATA=auto PAGE; RUN;
We have also seen that a SAS procedure can have one or more optional statements. Below we show that we can have one or more tables statements to specify the frequency tables we want, in this case, tables for rep78 and price. Because we used the page option, each table will start on a new page. This influences both the table made for rep78 and price. (Note that we could have specified tables rep78 price; and gotten the same result, but we wanted to illustrate having more than one tables statement.)
PROC FREQ DATA=auto PAGE; TABLES rep78 ; TABLES price ; RUN;
As we might expect, we could supply options on each of the tables statements to determine how those particular tables are shown. The example below requests frequency tables for rep78 and price, but the table for rep78 will omit percentages because it used the nopercent option. Both tables will appear on a new page (because the page option influences all of the tables) but only rep78 will suppress the printing of percentages because the nopercent option only applies to that one tables statement.
PROC FREQ DATA=auto PAGE; TABLES rep78 / NOPERCENT ; TABLES price ; RUN;
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