One study of cell phones and the risk of brain cancer looked

One study of cell phones and the risk of brain cancer looked at a group of 469 people who have brain cancer. The investigators matched each cancer patient with a person of the same age, gender, and race who did not have brain cancer, then asked about the use of cell phones. Result: “Our data suggest that the use of handheld cellular phones is not associated with risk of brain cancer.”31 Is this an observational study or an experiment? Justify your answer

Solution

This is observational study because we did not control the independent variable, i.e, we did not ask subjects to use cell phones or not use cellphones. We simply observed the cellphone usage of others, without experimenting with them.