1. Unit 5: Comparing Two Sample Means Lesson 1: The Paired Samples t Test EDER 6010: Statistics for Educational Research Dr. J. Kyle Roberts University of North Texas To Reject or Not to Reject? Next Slide

2. Paired Samples t Test The same people measured on the same construct on two different occasions Pre-test ↔ Post-test (a.k.a., Dependent Samples t Test) Assessing the effectiveness of a reading intervention with 8 students in a single classroom Next Slide

3. Null Hypothesis Next Slide -2 6 4 -2 7 5 -3 7 4 -2 8 6 -2 9 7 -1 8 7 -3 9 6 -3 8 5 Diff Post Pre

4. Paired Samples t Test in SPSS Analyze  Compare Means  Paired-Samples T Test Next Slide

5. Paired Samples t Test in SPSS Next Slide

6. SPSS Output Next Slide Mean of the difference scores

7. Comparing Studies t-crit = 2.093 on 19 df Which study is more likely to produce results that are statistically significant? t-crit = 1.980 on 120 df Study 2 Next Slide N = 20 N = 20 SD = 10 SD = 10 Mean = 90 Mean = 80 Posttest Pretest Study 1 N = 121 N = 121 SD = 10 SD = 10 Mean = 90 Mean = 80 Posttest Pretest Study 2

8. Comparing Studies t-crit = 2.093 on 19 df Which study is more likely to produce results that are statistically significant? Study 2 Next Slide N = 20 N = 20 SD = 10 SD = 10 Mean = 90 Mean = 80 Posttest Pretest Study 1 N = 20 N = 20 SD = 2 SD = 10 Mean = 90 Mean = 80 Posttest Pretest Study 2

9. Comparing Studies t-crit = 2.093 on 19 df Which study is more likely to produce results that are statistically significant? Study 1 Next Slide N = 20 N = 20 SD = 10 SD = 10 Mean = 90 Mean = 80 Posttest Pretest Study 1 N = 20 N = 20 SD = 10 SD = 10 Mean = 85 Mean = 80 Posttest Pretest Study 2

10. Factors Affecting t-calc 1. The magnitude of the difference between the two means 2. The “spreadoutness” of the scores 3. The number of people in the study 4. The level at which α is set Just like the Single-Sample t Test Next Slide

11. Unit 5: Comparing Two Sample Means Lesson 1: The Paired Samples t Test EDER 6010: Statistics for Educational Research Dr. J. Kyle Roberts University of North Texas To Reject or Not to Reject?