A study was initiated to investigate the effect of two drugs, administered simultaneously, on reducing human blood pressure. It was decided to use three levels of each drug and to include all nine combinations in the experiment. Nine high-blood-pressure patients were selected for the experiment, and one was randomly assigned to each of the nine drug combinations. The response observed was a drop in blood pressure over a fixed interval of time.
a. Is this a randomized block design?
b. Suppose that two patients were randomly assigned to each of the nine drug combinations. What type of experimental design is this?