In a study of cell phones and the risk of brain cancer, researchers studied a group of 469 people with brain cancer. They paired each person who had brain cancer with a person of the same sex, of similar age, and the same race who did not have brain cancer. Then they compared the cell phone use for each pair of people. The Journal of the American Medical Association published the results in 2000 in an article titled "Handheld Cellular Telephone Use and the Risk of Brain Cancer."

Pick the best description of this study:

Group of answer choices

an observational study of an association between two variables

an experiment to establish a cause-and-effect relationship between two variables

an observational study to make an estimate or a claim about a population