2. DEPENDENT SAMPLES t o Also called Paired t, Related Samples t o Purpose: Test whether two means are significantly different o Design: paired scores o within subjects o matched groups

3. Assumptions o Correlated (paired) observations o Normal distribution or large N o Interval or ratio level data

4. Computation of the Dependent Samples t

5. Computation of the Standard Error of the Difference

6. Example Five patients are exposed to both a placebo and an experimental treatment (at different times). They are measured on severity of symptoms. Was there a significant difference between conditions? (scores on next page)

7. M P = 12.40M E = 10.60 Patient#PE 1108 21410 31213 41515 5117

8. #PED 11082 214104 31213-1 415150 51174 STEP 1: Find the D scores.

9. DD- M D (D- M D ) 2 2.20.04 4 2.204.84 -1-2.807.84 0-1.803.24 4 2.204.84 M D =1.80  = 20.80 STEP 2: Find the s diff

10. STEP 2 Continued: Find the s diff

11. STEP 3: Compute the standard error.

12. STEP 4: Compute the t.

13. STEP 5: Look up t-critical in the table. df = N - 1 (N is the # of pairs of scores.) df = 5-1 = 4 two-tailed,  =.05 t-crit = 2.776

14. STEP 6: Compare t to t-critical. t = 1.76, t-crit = 2.776

15. APA Format Sentence A dependent samples t-test showed no significant difference between conditions, t (4) = 1.76, p >.05.

16. Computing Effect Size