1. 95% CI and Width for Mean # of hrs watching TV for Three Different Sample Sizes Sample SizeConfidence Interval Interval WidthStand DevStand Error N=1952.65-3.270.622.260.16 N=5042.76-3.160.402.260.10 N=1,9872.86-3.060.202.260.05

2. Part IV Significantly Different Using 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. Chapter 7 7 Doing the t test Prozac GroupPlacebo Group 5364 4268 5884 3965 4050 60 6181 4476

8. Chapter 7 8 Doing the t test Steps in the process Step 1:  Calculate Step 2:  Calculate

9. Chapter 7 9 Doing the t test Steps in the process Step 3:  Count the number of scores in each group. N 1 = # scores in Group 1. N 2 = # scores in Group 2.

10. Chapter 7 10 Doing the t test Steps in the process Step 4:  Calculate sample variance for both groups Step 5 : Do the math!! Be sure to solve within brackets first!!

11. Chapter 7 11 Significance testing Steps in the process Step 1:  Calculate the degrees of freedom N 1 + N 2 – 2 Step 2:  One- or two-tailed test of significance? Did you have a directional hypothesis or not?

12. Chapter 7 12 Significance testing Steps in the process Step 3:  Using the table, find the critical values of t using N 1 + N 2 – 2 degrees of freedom.  Page 353-355, the t distribution. Step 4:  Compare the obtained t with the critical value of t.

13. Chapter 7 13 You Try!! Participant ID PlaceboParticipant ID Treatment 13591128 14371234 15421726 20301836 23371923 24512224 29552636 30462726

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?