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. We call the National Halothane Study an observational study rather than an experiment because an observational study tries to gather information without disturbing the scene.

b. The explanatory is the type of anesthetic and the response variable is the death rate in this study.

c. The concept of confounding in this context and identifying a variable that might be confounded with the doctor’s choice of anesthetic is one possible confounding variable is a type of surgery. If one anesthesia is used more often with a type of surgery has a higher death rate anyway. We wouldn't know if the death rate was higher because of the anesthesia type or the surgery type.

Step-by-step solution

Part (a) step 1: Given Information

We need to explain whether 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.

Part (a) step 2: Explanation

Here,

The experiment deliberately imposes some treatment on individuals in order to observe the responses.

An observational study tries to gather information without disturbing the scene they are observing.

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

Part (b) step 1: Given Information

We need to identify the explanatory and response variables in this study.

Part (b) step 2: Explanation

A response variable is a variable that measures an outcome or result of a study, while an explanatory variable is a variable that we think explains or causes changes in the response variables.

We expect a different anesthetic to affect the death rate, which implies that the explanatory variable is a type of anesthetic and the response variable is the death rate.

Part (c) step 1: Given Information

We need to explain the concept of confounding in this context and identify a variable that might be confounded with the doctor’s choice of anesthetic.

Part (c) step 2: Explanation

Variables are confounded when the effects on a response variable can't be distinguished.

One possible confounding variable is the type of surgery. If one anesthesia is used 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 anesthesia type or the surgery type.