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The TTEST Procedure

Example 67.2: One-Sample Comparison Using the FREQ Statement

This example examines children's reading skills. The data consist of Degree of Reading Power (DRP) test scores from 44 third-grade children and are taken from Moore (1995, p. 337). Their scores are given in the following DATA step.

   title 'One-Mean Comparison Using FREQ Statement';
   data read;
      input score count @@;
      datalines;
   40 2   47 2   52 2   26 1   19 2
   25 2   35 4   39 1   26 1   48 1
   14 2   22 1   42 1   34 2   33 2
   18 1   15 1   29 1   41 2   44 1
   51 1   43 1   27 2   46 2   28 1
   49 1   31 1   28 1   54 1   45 1
   ;
   run;

The following statements invoke the TTEST procedure to test if the mean test score is equal to 30. The count variable contains the frequency of occurrence of each test score; this is specified in the FREQ statement.

   proc ttest data=read h0=30;
      var score;
      freq count;
   run;

The output, shown in Output 67.2.1, contains the results.

Output 67.2.1: TTEST Results

One-Mean Comparison Using FREQ Statement

The TTEST Procedure

Frequency: count

Statistics
Variable N Lower CL
Mean
Mean Upper CL
Mean
Lower CL
Std Dev
Std Dev Upper CL
Std Dev
Std Err Minimum Maximum
score 44 31.449 34.864 38.278 9.2788 11.23 14.229 1.693 14 54

T-Tests
Variable DF t Value Pr > |t|
score 43 2.87 0.0063


The SAS log states that 30 observations and two variables have been read. However, the sample size given in the TTEST output is N=44. This is due to specifying the count variable in the FREQ statement. The test is significant (t=2.87, p=0.0063) at the 5% level, thus you can conclude that the mean test score is different from 30.

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