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95% CI and Width for Mean # of hrs watching TV for Three Different Sample Sizes

Learn to perform t-tests on related groups, compute t-values, interpret results, and determine significance in Chapter 11.

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95% CI and Width for Mean # of hrs watching TV for Three Different Sample Sizes

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  1. 95% CI and Width for Mean # of hrs watching TV for Three Different Sample Sizes

  2. Part IVSignificantly DifferentUsing Inferential Statistics Chapter 11    t(ea) for Two (Again) Tests Between the Means of Related Groups

  3. What you will learn in Chapter 11 • When to use a t test for independent means • How to compute the observed t value • Interpreting the t value and what it means

  4. t Tests for Dependent Samples • Determining the correct statistic

  5. Computing the Test Statistic • Numerator reflects the sum of the differences between two groups

  6. Degrees of Freedom • Degrees of freedom approximate the sample size • Degrees of freedom can vary based on the test statistic selected • For this procedure… • n – 1 (where n is the number of observations)

  7. Doing the t test

  8. Doing the t testSteps in the process • Step 1: • Calculate • Step 2: • Calculate

  9. Doing the t testSteps in the process • Step 3: • Count the number of scores in each group. • N1 = # scores in Group 1. • N2 = # scores in Group 2.

  10. Doing the t testSteps in the process • Step 4: • Calculate sample variance for both groups Step 5: Do the math!! Be sure to solve within brackets first!!

  11. Significance testingSteps in the process • Step 1: • Calculate the degrees of freedom • N1 + N2 – 2 • Step 2: • One- or two-tailed test of significance? • Did you have a directional hypothesis or not?

  12. Significance testingSteps in the process • Step 3: • Using the table, find the critical values of t using N1 + N2 – 2 degrees of freedom. • Page 353-355, the t distribution. • Step 4: • Compare the obtained t with the critical value of t.

  13. You Try!!

  14. So How Do I Interpret… • t(24) = 2.45, p > .05 • t represents the test statistic used • 24 is the number of degrees of freedom • 2.45 is the obtained value (from the formula) • p > .05 indicates the probability

  15. Using the Computer • SPSS and Pared Samples t Test

  16. SPSS Output • What does it all mean?

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