Question: A medical engineer has constructed a machine to simulate the human heart and study the effect of …

A medical engineer has constructed a machine to simulate the
human heart and study the effect of valve type and pulse rate on
heart durability. The machine can be equipped with 3 different
valve types and set at 3 different pulse rates. The machine can
simulate 3 hearts at one time (sub-units), with three runs at
different times (whole-units) to accommodate the 9 treatment
combinations. Therefore the investigator is using a split plot
design to conduct the experiment. For each of the following
situations, which factor should be assigned to sub-unit:

A. The investigator is most interested in detecting differences
among valve types and less interested in differences among pulse
rates.

B. Changing pulse rates can be done by a simple flip of a
switch, while changing the valve type requires several hours of
work.

C. The investigator expects large differences among valve types
and relative small differences among pulse rate.