t test for matched samples

1. t test for matched samples Matched Samples: Samples that have subjects chosen based on shared characteristics.

2. Typical matching characteristics: - Gender - Socioeconomic status (SES) - Age - IQ

3. Matching subjects reduces variability that is caused by the matching variable.

4. D : difference between scores of matched subjects.

5. ( sum of the differences) (# of matched pairs, or # of difference scores)

6. : standard error of the differences Standard deviation of the difference scores # of difference scores or # of pairs of scores

7. Standard deviation of the differences:

8. Steps for a t test for matched samples: 1) find differences between matched pairs Sample One Sample Two Sub. 1 25 22 Sub. 2 45 40 Sub. 3 30 31 Sub. 4 15 11 Sub. 5 28 22

9. 1) find differences between matched pairs Sample One Sample Two D Sub. 1 25 22 3 Sub. 2 45 40 5 Sub. 3 30 31 - 1 Sub. 4 15 11 4 Sub. 5 28 22 6  D = 17

10. 2) find average difference

11. 3) find standard deviation of the differences D D2 3 9 5 25 - 1 1 4 16 6 36  D2 = 87

16. 4) computed standard error of the differences

18. 5) compute and evaluate t

19. Computed t = 2.833 df = n - 1 or 4 Critical value = 2.776