Chapter 4, Problem 6CRE

a.

To determine

To explain: The reason of calling the study of National Halothane an observational study instead of experimental study

Explanation of Solution

Given:

Anaesthetic	A	B	C	D
Death rate (%)	1.7	1.7	3.4	1.9

Here, the researchers are not influencing the outcome by randomly assigning the subjects to treatment or control groups, but instead observing the death rates. Therefore, the study is observational.

b.

To determine

To explain: The effect of lurking variable in confounding.

Explanation of Solution

From the above part, it is known that the study is an observational study. So, many confounders are possible here. One of the possible confounders is the surgery. The death rate may be high due to the use of some medicine and it is impossible to know if the date rate is high due to the surgery or the use of some medicine.