For the following two sets of computer outputs, write first an interpretation of the data and then briefly explain. The first example is from an independent-groups t test and the second from a correlated test. Assume that you are seeing the results of a memory test with group 1 receiving a new medication and group 2 being the control (Placebo) group. A higher mean is equivalent to an on average higher score on the memory test. In the correlated study (b), the matched pairs approach was used, matching participants by gender, age and an overall health score:
a) Group 1: M = 59.21 SD = 12.32 Standard Error = 2.43
Group 2: M = 32.45 SD = 10.91 Standard Error = 3.18
F = 2.13 p = 0.32
t = 2.89, df = 18, (also written in an computer output as t(18) = 2.89 ); p = 0.02
d = 0.89
b) Write an interpretation of the following data for a correlated-groups t test and also briefly explain:
Group 1: M = 59.21 SD = 12.32
Group 2: M = 32.45 SD = 10.91
Correlation = 0.810 p = 0.03
t = 2.89, df = 9, (also written in an computer output as t(9) = 2.89 ); p = 0.02
d = 0.89
c) Discuss for a and b separately: Were significant differences found? (Again, review in chapter 10 the two paragraphs titled "Translating Statistics into Words" - provides example for t-test for independent groups and another for t-test for correlated samples)
d) Compare the degrees of freedom in a and b. Why are the degrees different even if both studies had the same number of participants? Based on the degrees, how many participants were in each experiment? Review effect size. How do you interpret the d value in this example for the independent group design? (different formula for d in the correlated design)
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