Chapter 4, Problem R4.5RE

(a)

To determine

To explain why you call the National Halothane study an observational study rather than an experiment even though it compared the results of using different anaesthetics in actual surgery.

Explanation of Solution

The National Halothane study an observational study rather than an experiment even though it compared the results of using different anaesthetics in actual surgery because An experiment deliberately imposes some treatment on individuals in order to observe their responses.An observational study tries to gather information without disturbing the scene they are observing.

Since records are used, no treatment was deliberately imposed on individuals and thus the study is an observational study.

(b)

To determine

To identify the explanatory and response variable in the study.

Answer to Problem R4.5RE

The experimental variable is the anaesthetics and the response variable is the effect of the anaesthetic that is the death rate.

Explanation of Solution

The explanatory variable is the one that is changed in order to see the effect on the response variable.

The experimental variable is the anaesthetics used in the surgery because it is used in the experiment and its result is the response variable is the effect of the anaesthetic that is the death rate controlled by the anaesthetics.

(c)

To determine

To explain the concept of confounding in this context and identify a variable that might be confounded with a doctor’s choice of anaesthetics.

Answer to Problem R4.5RE

The type of the surgery is the variable.

Explanation of Solution

Variables are confounded when their effects on a response variable cannot be distinguished. One possible confounding variable is type of surgery. If one anaesthesia is used more often with a type of surgery that has a higher death rate anyway, we wouldn’t know if the death rate was higher because of the anaesthesia type or the surgery type.