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 Pretest Data

Step 7: Complete the sum of squares (SS)calculation.

The sum of squares is the sum of squared deviations from the mean.

The formula is:

The different parts of the formula have been calculated in steps 5 and 6:

1. The first part of the formula corresponds to step 6:
2. The numerator of the second part was calculated in step 5:
3. The denominator, n, represents the total number of participants.

For our example, both the participants and comparison group have 50 members. Our next step is to insert all the numbers in the formula.

Sum of squares (SS) calculation for the participant group:

SS = 278 - (6724/50) = 278 - 134.48 = 143.52

Sum of squares (SS) calculation for the comparison group:

SS = 297 - (5929/50) = 297 - 118.58 = 178.42