1. Determine whether each of the following is an experiment or an observational study. Also identify the explanatory and response variables.

a. Sixty patients with carpal tunnel syndrome are randomly divided into 2 groups. One group is treated weekly with both acupuncture and an exercise program. The other is treated weekly with the exact same exercise regimen, but no acupuncture. After one year, both groups are questioned about their pain from the carpal tunnel syndrome.

b. Researcher Eric N. Taylor and others wanted to determine if weight, weight gain, body mass index (BMI), and weight circumference are associated with kidney stone formation. To make this determination, they looked at 4,827 cases of kidney stones covering 46 years. Based on an analysis of the data, they concluded that obesity and weight gain increase the risk of kidney stone formation.

c. Researcher Helle Collatz Christensen and co-workers examined the possible association between the use of cellular phones and the development of acoustic neuroma (a non-cancerous growth in the inner ear) by comparing 106 cases of individuals with acoustic neuroma to 212 cases of individuals who did not have acoustic neuroma . The data obtained included information on the use of cellular telephones from personal interviews, data from medical records, and the results of radiological exams.

d. A sample of 504 patients in the early stages of Alzheimer's disease is randomly divided into two groups. One group receives an experimental drug regimen, while the other group receives a placebo regimen. The advance of the disease in the patients is tracked at 1-month intervals over the next year.