a medical doctor randomly assigns individuals into two groups, giving one group a new drug to reduce blood pressure and the other group a placebo, in order to study the effects of the new drug. an economist uses survey data from the bureau of labor statistics to study the relationship between age and annual salary. an oncologist randomly assigns rats into two groups, giving one group a new drug intended to fight cancer and giving the other group a placebo, in order to study the effects of the new drug.



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