Which of the following is an example of correlated observations? You may choose more than 1 correct answer.
Select one or more:
a. Comparing the gene expression levels in tumor tissue and normal tissue from the same people.
b. Comparing the gene expression profiles of 50 people who have cancer and 50 people who are cancer-free.
c. Comparing quality of life scores in twins with cancer to quality of life scores in their disease-free identical twins.
d. Comparing two groups of people who either applied SPF-85 sunscreen to their faces or applied SPF-50 sunscreen to their faces.