A researcher would like to find out if relaxation training will affect number of headaches for chronic headache sufferers. For the week prior to training, each participant records number of headaches suffered. Participants then receive relaxation training, and for week following training the number of headaches is again measured. The change in number of headaches before and after training is as follows (minus signs point out reduction).
Difference scores: -5 -1 -4 -3 -6 -8 0 +1 -1
a) Evaluate the mean and SS for the sample of difference scores.
b) Do results indicate significant difference? Employ a two-tailed test with α = .05.
a) Yes, relaxation training has significant effect.
b) No, the relaxation training hasn't any significant effect.
(c) Evaluate r^{2}, the percentage of variance accounted for, to measure the size of effect. (Round the answer to two decimal places.)
r^{2} =