Marathon runners were randomly assigned to receive either vitamin C or a placebo.

Separately, these treatments were also randomly assigned to a group of nonrunners the same age as the runners. All subjects were watched for 2 weeks after the race to see if infections developed.

1. What is the name for this experimental design? I think it is either randomized comparative design or compeltely randomized design. Can you please explain and help me out? Thank you

Could it be a block design?

Thank you

Yes.

The experimental design you described is called a randomized comparative design, also known as a randomized controlled trial (RCT). In this design, participants are randomly assigned to different treatment groups to compare the effects of the treatments on the outcome of interest.

In your case, marathon runners were randomly assigned to receive either vitamin C or a placebo. This is the randomized part of the design, as the assignment of treatments is done randomly, ensuring that each participant has an equal chance of being assigned to either group. Random assignment helps to eliminate any potential biases and ensures that the treatment groups are comparable.

The comparative part of the design involves comparing the effects of the different treatments. By assigning some participants (the marathon runners) to receive vitamin C and others to receive a placebo, researchers can compare the rates of infection between the two groups. This comparison allows for evaluating the effectiveness of vitamin C in preventing infections for marathon runners.

So, in conclusion, the design you described is a randomized comparative design because it involves randomly assigning participants to different treatment groups and comparing the effects of these treatments on the outcome of interest.