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

Independent Samples t-Test for Pretest Data

Let's try to find some good news for Jack. First, we need to determine if the participant and comparison groups were comparable regarding their inhalant use. This is called baseline equivalence.

We will do this by comparing participants and comparisons at pretest. Since we are looking at DIFFERENT groups at the same time, we use the t-test for independent samples.

This t-test will let us know whether the two groups were comparable at the beginning of the program. The difference should not be statistically significant.

Before we run the t-test, we need the means for the comparison group, since the evaluator did not include this information in the original evaluator's report. We calculated the means earlier. Here they are again.

Now that we have the means, let's look at a graph of them. This shows the relationship between the two groups.