Whiter Teeth An ad for Crest White strips Premium claims that the strips will whiten teeth in 7 days and the results will last for 12 months. A researcher who wishes to test this claim studies 20 sets of identical twins. Within each set of twins, one is randomly selected to use Crest White strips Premium in addition to regular brushing and flossing, while the other just brushes and flosses. Whiteness of teeth is measured at the beginning of the study, after 7 days, and every month thereafter for 12 months.
(a) What type of experimental design is this?
(b) What is the response variable in this experiment?
(c) What are the treatments?
(d) What are other factors (controlled or uncontrolled) that could affect the response variable?
(e) What might be an advantage of using identical twins as subjects in this experiment?
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