Question: A researcher would like to determine if relaxation training will affect the number of headaches for chronic headache sufferers. For a week prior to training, each participant records the number of headaches suffered. Participants then receive relaxation training, and for the 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 indicate a reduction):

Difference scores: -5 -1 -4 -3 -6 -8 0 +1 -1

Compute r² to measure the size of the effect.