A researcher wants to conduct a study to see if cell phones cause headaches. The researcher finds 30 individuals who use cell phones regularly and 30 that do not. Each of the 60 individuals are given a questionnaire designed to determine headache frequency. If the 60 individuals did not know they were participating in the study, which statement about the study is correct? a. It is an experiment where cell phone habits is a blocking variable.
b. It is an observational study.
c. It is a matched-pairs design.
d. It is a randomized experiment.
e. It is a double-blind study.