[ Medicine ] Open Question : Which variable(s) should be standard across all treatment groups?

You are designing an experiment to test the effect of a new high blood pressure drug. You will have 1,000 participants divided into three groups: 300 people will be in a control group receiving a pill that has no active ingredient; 350 people will receive a low dose of the new drug; 350 people will receive a high dose of the new drug. Which variable(s) should be standard across all treatment groups? Choose one or more: A. the amount of drug each participant in a test group receives B. the blood pressure measurement of all the participants during the experiment C. perfectly healthy blood pressure levels D. the approximate age of the participants E. the general state of health of all the participants

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