Question

The National Halothane Study was a major investigation of the safety of anesthetics used in surgery. Records of over $850,000$operations performed in $34$major hospitals showed the following death rates for four common anesthetics:

There seems to be a clear association between the anesthetic used and the death rate of patients. Anesthetic C appears to be more dangerous.

a. Explain why we call the National Halothane Study an observational study rather than an experiment, even though it compared the results of using different anesthetics in actual surgery.

b. Identify the explanatory and response variables in this study.

c. When the study looked at other variables that are related to a doctor’s choice of anesthetic, it found that Anesthetic C was not causing extra deaths. Explain the concept of confounding in this context and identify a variable that might be confounded with the doctor’s choice of anesthetic.

Short answer

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

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

c. The type of the surgery is the variable.

Step-by-step solution

Part (a) Step 1. Explanation

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.

Part (b) Step 1. Explanation

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.

Part (c) Step 1. Explanation

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.