Look, Ma, no hands! Does talking on a hands-free cell phone distract drivers? Researchers recruit $40$student subjects for an experiment to investigate this question. They have a driving simulator equipped with a hands-free phone for use in the study.

(a) Researchers are considering the design shown in the figure below. What type of design is this?

(b) Explain how blocking could be used to improve the design in (a).

(c) Why is it important to randomly assign the treatments within each block?

Researchers wants to find out if taking on hands free cell phone distracts the driver. The below design is considered:

They have a driving simulator equipped with a hands free phone.

It is complete randomized design because it splits the group into two smaller groups randomly. One receives treatment driving and other receives treatment driving and talking.

Blocking can improve design by:

• Letting each student as blocks run the simulator twice, once with phone and once without phone in random order as matched pair design.
• It controls variability among students in driving. In this way, it will improve the design.

It is important to randomly assign treatment within each block as they can perform better in second attempt due to more experience. Also it will allow both treatments to occur which will let us compare the two results knowing that experience can improve the results.