MODULE 5

The following covers some of the most commonly used SAS procedures with which you can run some basic statistical analyses. Use the File, Import Data... to import the Example Data 1 file using the Import Wizard with SPSS File (*.sav) source and member name example1 as was done previously.

1. PROC CORR

In SAS, we use PROC CORR to examine bi-variate relationships.

PROC CORR DATA=example1;
VAR age recall1 recall2;
RUN;

If we had missing data in at least one of the variables, then we could use a 'nomiss' optional statement to do listwise deletion. As an example, use the Import Wizard to import the Example Data 2 file using the Excel File (*.xls) source as was done previously. Remember to use 'example2' as the member name to differentiate it from example1.

PROC CORR DATA=example2;
VAR age recall1 recall2;
RUN;

PROC CORR DATA=example2 NOMISS;
VAR age recall1 recall2;
RUN;

2. Chi-square tests using PROC FREQ

We can use proc freq to examine class standing (cl_st, where 1 = freshman, 2 = sophomore, 3 = junior, & 4 = senior) by Sex (males coded 1, females coded 0).  Using the chi2 option we can request a chi-square test that tests if these two variables are independent, as shown below.

PROC FREQ DATA=example1;
  TABLES cl_st*Sex / CHISQ;
RUN;

We can also get the Fisher's exact test statistic using the modifier EXACT.

PROC FREQ DATA=example1;
  TABLES cl_st*Sex / CHISQ EXACT ;
RUN;

3. PROC TTEST

We can use PROC TTEST to examine differences between two groups. Notice in the output, we get t-values for variances assumed equal and variances not assumed equal.

First, we can run an independent groups t-test.

PROC TTEST DATA=example1;
  CLASS candy;
  VAR recall1;
RUN;

Second, we can run a dependent groups t-test (sometimes called: related groups t-test, paired samples t-test, or repeated measures t-test).

PROC TTEST DATA=example1;
  PAIRED recall1*recall2;
RUN;

Third, we can run the seldom used single sample t-test (here the null supposes the true mean of recall 1 = 15).

PROC TTEST DATA=example1 HO=15;
VAR recall1;
RUN;

Return to the SAS Short Course