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

The t-Test of Differences Between Means:
Independent Samples t-Test for Posttest Data

Step 8: Calculate the degrees of freedom.

The formula for degrees of freedom is n -1. For our example, the group of participants consists of 50 members, so the degrees of freedom for this group = 50 - 1 = 49. Likewise, n - 1 or 50 - 1 gives 49 degrees of freedom for the comparison group. Once the degrees of freedom are calculated, we need to add them: 49 + 49 = 98.