Chronic Achilles tendon pain (i.e., tendinosis) is common among middle-aged recreational athletes. A group of Swedish physicians investigated the use of heavy-load eccentric calf muscle training to treat Achilles tendinosis (British Journal of Sports Medicine, Feb. 1, 2004). A sample of 25 patients with chronic Achilles tendinosis undertook the treatment. Data on tendon thickness (measured in millimeters) were collected by ultra-sonography both before and following treatment of each patient. The researchers want to compare the mean tendon thickness before treatment with the mean tendon thickness after treatment.
a. Is this a designed experiment or an observational study? Explain.
b. What is the experimental unit of the study?
c. What is the response variable of the study?
d. What are the treatments in this experiment?