A medical research group has designed two different drugs, drugs A and B, to treat high blood pressure. They are at the stage of testing which drug is more effective and at which dose. They want to run a trial with 120 patients currently suffering from high blood pressure at the doses of 10mg, 15mg and 20mg per day of the active ingredient of each drug for a period of three months.

(a) What are the explanatory and response variables in this study?

(b) Design a completely randomised experiment for this study, in which each patient receives only one drug at one dose only. Comment on elements of control, randomisation and replication in your design. Your answer should include a schematic diagram or flow chart.

(c) Say exactly what would be measured and what comparisons you would make at the end of the experiment.