CONTENTS

Table of Contents
Introduction

1. Descriptive Statistics in Evaluation
2. Subgroup Analysis
3. Variable - Are They Related?
4. Correlation
5. The t-Test of Difference Between Means

Supplements
Resources
Glossary

Wading Through the Data Swamp:
Program Evaluation 201

Results for the Paired t-Test

When looking at the table, we found that the value for our degrees of freedom, 49, was not included. Thus, no specific critical value is available. However, when this happens, you can use the critical values listed for the lower and upper values of the range in which the degrees of freedom value falls.

The critical value for 49 degrees of freedom would fall between 2.021 and 2.000. The critical values of 2.021 and 2.000 correspond to 40 and 60 degrees of freedom, respectively. Our calculated t-value of 2.3 is greater than the t-critical, which would be between 2.021 and 2.000. Therefore, we conclude that the pretest means and the posttest means for the participants are significantly different.

Jack could say, " I found that a statistically significant difference exists between the mean of the pretest for the participants and the mean of the posttest for the participant group."

Therefore:

Null hypothesis

H₀ = The mean score for inhalant use for participants at posttest is not different from the mean score for inhalant use for participants at pretest.
OR
H₀ = The mean difference between the two groups is zero ("null").
OR
H₀ = There is no difference between the means of the two groups. The symbolic representation is H₀ = µ1 - µ2 = 0.

Research hypothesis

H₁ = The mean score of inhalant use for participants at posttest is different from the mean score of inhalant use for participants at pretest.
OR
H₁ = The mean difference between the two tests is not zero.
OR
H₁₌There is a difference between the means of the two groups. The symbolic representation is H₁ = µ1 - µ2 not equal 0.

Jack's evaluator concluded, based on this t-test, that the Cool After School Program did not appear to be effective in reducing participants' inhalant use. Inhalant use did not decrease from pretest to posttest. Instead, average or mean inhalant use increased after the program.