5.in order to determine if smoking causes cancer, researchers surveyed a large sample of adults.For each adult, they recorded whether the person had smoked regularly at any period in their life and whether the person had cancer.They then compared the proportion of cancer cases in those who had smoked regularly at some time in their lives with the proportion of cases in those who had never smoked regularly at any point in their lives.The researchers found that there was a higher proportion of cancer cases among those who had smoked regularly than among those who had never smoked regularly.What type of study is this?

A. An observational study

B. A double-blind experiment

C. An experiment, but not a double-blind experiment

D. A block design

ANSWER:

REASON:

6. Will a fluoride mouthwash used after brushing reduce cavities?Twenty sets of twins were used to investigate this question.One member of each set of twins used the mouthwash after each brushing, the other did not.After 6 months, the difference in the number of cavities of those using the mouthwash was compared with the number of cavities of those who did not use the mouthwash.What type of study is this?

A. An observational study

B. A double-blind experiment

C.An experiment, but not a double-blind experiment

D. A matched-pairs experiment

ANSWER:

REASON:

7.Sickle-cell disease is a painful disorder of the red blood cells that in the United States affects mostly black persons.To investigate whether the drug hydroxyurea can reduce the pain associated with sickle-cell disease, a study by the National Institutes of Health gave the drug to 150 sickle-cell sufferers and a placebo to another 150.Neither the participants nor the researchers knew who had received each type of treatment. The researchers then counted the number of episodes of pain reported by each subject.What type of study is this?

A. An observational study

B. A double-blind experiment

C. A single-blind experiment

D. A matched-pairs experiment

ANSWER:

REASON: