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Chapter 11: The t Test for Two Related Samples

Chapter 11: The t Test for Two Related Samples. Related t Formulas. Group Assignment of Subjects Matched by IQ. Before and after treatment differences. Formulas for Related Samples t. (Where n = number of difference scores). Population of difference scores.

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Chapter 11: The t Test for Two Related Samples

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  1. Chapter 11: The t Test for Two Related Samples

  2. Related t Formulas

  3. Group Assignment of Subjects Matched by IQ

  4. Before and after treatment differences

  5. Formulas for Related Samples t (Where n = number of difference scores)

  6. Population of difference scores Process of related samples testing D scores µD = ? Make inference about µD Obtain sample

  7. Scores on Depression Inventory Before and After Treatment

  8. Depression Study -30 254

  9. Depression study cont.

  10. Depression Study t computation

  11. What is the effect of relaxation training on severity of asthma symptoms: • Measure the number of doses of medication needed to counter asthma attacks (over 1 week) Relaxation Training • Measure the number of doses of medication needed to counter asthma attacks (over 1 week)

  12. 1. Ho: µD = 0 (No change in symptoms) Asthma Study H1: µD ≠ 0 (There is a change…)  = 0.05 2. tcrit(4) = + 2.776 3. 4. Reject Ho because tobt of -3.72 < tcrit of -2.776 5. Conclusion: Relaxation training significantly reduced the number of asthma attacks, t(5) = -3.72, p < 0.05.

  13. Critical regions for asthma study Reject Ho Reject Ho -2.776 0 +2.776

  14. Asthma Study Data Table

  15. One tailed critical region (df =4) df = 4 Reject Ho -2.132

  16. Reading Program Data Table

  17. Treatment 1 vs. 2 Data Table

  18. Assumptions for Related-Samples t test • Observations within each treatment must be independent • The population distribution of difference scores must be normal • Note: #2 is not a concern as long as sample size is 30 or less

  19. Before and after data table 1

  20. Before and After data table 2

  21. Reading Program vs. Control Data Table

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