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

Steps for Calculating a Paired Sample t-Test for Participant Pre- and Posttests

• Step 1: State null hypothesis
• Step 2: Choose a significance level
• Step 3: Subtract the pretest scores from the posttest scores and add the results.
• Step 4: Calculate the mean for the sum of the differences between posttest scores and pretest scores.
• Step 5: Square the sum of the X values. Then divide by the n value.
• Step 6: Square the differences between posttest scores and pretest scores and add the results.
• Step 7: Complete the sum of squares (SS) calculation.
• Step 8: Divide the sum of squares by the degrees of freedom to get the variance - (^S2)
• Step 9: Take the square root of the variance divided by n.
• Step 10: Use the t-test formula: Divide the mean of X from step 4 by the square root of the variance from step 8 divided by n.
• Step 11: Compare the calculated t-value with the critical t-value found in the table.