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

Paired t-Test or Independent t-Test?

1. t-test for paired samples. The SAME group of people are compared at two different times (e.g., participants before and after the program). A group's posttest score is generally more like their own pretest score than any randomly chosen posttest score. So there is generally a correlation between pretest and posttest scores.
2. t-test for independent samples. DIFFERENT groups of people are compared at the same point in time (e.g., participants and comparisons after the program).

We will perform three different t-tests:

1. Paired t-test to compare the participant pre- and posttest scores (same group at different times)
2. Independent t-test to compare the participants and comparisons at pretest (different groups at the same time)
3. Independent t-test to compare participants and comparisons at posttest (different groups at the same time)

We have identified 11 steps to perform the t-tests manually for the Cool After School Program. The formula for the paired and independent sample t-tests is NOT the same, so make sure you understand the difference.