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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';
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 CLMean Mean Upper CLMean Lower CLStd Dev Std Dev Upper CLStd 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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